Semiconductor device and a method of manufacturing the same

ABSTRACT

In connection with a semiconductor device including a capacitor element there is provided a technique capable of improving the reliability of the capacitor element. A capacitor element is formed in an element isolation region formed over a semiconductor substrate. The capacitor element includes a lower electrode and an upper electrode formed over the lower electrode through a capacitor insulating film. Basically, the lower electrode and the upper electrode are formed from polysilicon films and a cobalt silicide film formed over the surfaces of the polysilicon films. End portions of the cobalt silicide film formed over the upper electrode are spaced apart a distance from end portions of the upper electrode. Besides, end portions of the cobalt silicide film formed over the lower electrode are spaced apart a distance from boundaries between the upper electrode and the lower electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2007-267398 filed onOct. 15, 2007 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and amanufacturing technique for the same. Particularly, the presentinvention is concerned with a semiconductor device having a capacitorelement and a technique applicable effectively to the manufacture of thesemiconductor device.

In Japanese Unexamined Patent Publication No. 2003-100887 (PatentLiterature 1) there is described a technique for improving thereliability of an upper-layer electrode/lower-Layer electrode structureformed with an insulating film therebetween. More particularly, alower-layer electrode and an upper-layer electrode are stacked in thisorder on a silicon substrate. In this case, a contact hole for theupper-layer electrode, which hole is for coupling the upper-layerelectrode to an overlying wiring layer, is formed in a region positionedabove an isolation region which is formed separately from thelower-layer electrode.

In Japanese Unexamined Patent Publication No. 2003-124356 (PatentLiterature 2) there is described a technique related to a semiconductordevice such as a flash memory having a capacitor element used forexample in a charge pump circuit, whereby an increase of chip area issuppressed, the capacitance of the capacitor element can be set highlyaccurately, and the number of manufacturing steps can be reduced. Moreparticularly, on a field oxide film there is formed a lower electrode ofthe capacitor element under self-aligning with a trench portion. By sodoing, according to Patent Literature 2, the lower electrode and afloating gate electrode in a memory cell portion can be formedsimultaneously in the same process. The lower electrode is enclosed witha trench portion formed in a field oxide film. An upper electrode formedin the same process as a control gate electrode is formed on the lowerelectrode through an insulating film formed in the same process as agate-to-gate insulating film in the memory cell portion. In thistechnique, the upper electrode is extended to the exterior of the lowerelectrode and in this extended region there is formed a plug coupled tothe upper electrode.

In Japanese Unexamined Patent Publication No. 2002-313932 (PatentLiterature 3) there is described, in connection with a semiconductordevice having a capacitor element, a technique for preventing theoccurrence of short-circuit caused by silicide and leak current in sidewall portions formed on side portions of a capacitor electrode. Moreparticularly, a lower capacitor electrode, a capacitor insulating filmand an upper capacitor electrode are formed on an element isolationregion of a silicon substrate. Thereafter, a silicon oxide film isformed on the whole of an upper surface of the silicon substrate. Ontothis silicon oxide film is then formed a resist pattern which coversfrom a certain range inside an edge portion of the upper capacitorelectrode up to a certain range outside the edge portion. Then,anisotropic etching is performed to form side walls which cover sidefaces of the lower capacitor electrode and side walls which cover sidefaces and an edge portion of an upper surface of the upper capacitorelectrode. Thereafter, a metal silicide film is formed on surfaces ofthe upper and lower capacitor electrodes not covered with the sidewalls.

PATENT LITERATURES

1. Japanese Unexamined Patent Publication No. 2003-100887

2. Japanese Unexamined Patent Publication No. 2003-124356

3. Japanese Unexamined Patent Publication No. 2002-313932

SUMMARY OF THE INVENTION

There is a semiconductor device wherein a microcomputer is formed on onesemiconductor chip. On the semiconductor chip with a microcomputerformed thereon there are formed a central processing unit (CPU)comprised of a logic circuit such as a CMISFET (Complementary MetalInsulator Semiconductor Field Effect Transistor), as well as a memoryand an analog circuit.

As the memory formed on the semiconductor chip there is used, forexample, an electrically rewritable non-volatile memory. EEPROM(Electrically Erasable and Programmable Read Only Memory) and flashmemory are in wide use as electrically writable and erasablenon-volatile memories. These non-volatile memories typified by EEPROMand flash memory which are in wide use now, have a charge storage filmsuch as an electrically conductive floating gate electrode or a trappinginsulating film, surrounded with a silicon oxide film, below a gateelectrode of MOS (Metal Oxide Semiconductor). Information is stored byutilizing the fact that the threshold value of transistor differsdepending on the state of charge storage of the floating gate electrodeor the trapping insulating film.

The trapping insulating film represents an insulating film having a traplevel capable of storing an electric charge. An example thereof is asilicon nitride film. By injection and release of an electric charge toand from the trapping insulating film the threshold value of MOStransistor is shifted, allowing the transistor to operate as a storageelement. A non-volatile memory using a trapping insulating film as acharge storage film is called a MONOS (Metal Oxide Nitride OxideSemiconductor) type transistor. This transistor is superior in thereliability of data hold because an electric charge is stored in adiscrete trap level, as compared with the case where an electricallyconductive floating gate electrode is used as the charge storage film.Moreover, because of the excellent data hold reliability, the siliconoxide films overlying and underlying the trapping insulating film can bemade thin, thus making it possible to lower the voltage in write anderase operations.

For operating such a non-volatile memory as described above, a drivecircuit such as a booster circuit is formed in the semiconductor chip. Ahighly accurate capacitor element is considered necessary for the drivecircuit. In the semiconductor chip with a microcomputer formed thereonthere also is formed an analog circuit. A highly accurate capacitorelement is considered necessary also for the analog circuit. Thus, inthe semiconductor chip there also is formed a capacitor element inaddition to the foregoing non-volatile memory and MISFET.

The capacitor element is formed for example in a wiring layer. Moreparticularly, there is known a structure wherein an insulating filmpresent between wiring layers is used as a capacitor insulating film andupper and lower electrodes are formed by a metal film used in wiring.For example, this capacitor element is called MIM (Metal InsulatorMetal) capacitor element. According to the MIM capacitor element I ispossible to form a highly accurate capacitor element because the metalfilm for wiring is used for both upper and lower electrodes.

However, the formation of MIM capacitor requires an additional processfor forming the same capacitor, thus giving rise to the problem that thecost of the semiconductor device increases. In view of this point therehas been proposed a technique of forming the capacitor element on asemiconductor substrate.

For example, in a non-volatile memory cell, a control gate electrode isformed on a semiconductor substrate through a gate insulating film, andon one side wall of the control gate electrode is formed a sidewall-like memory gate electrode through a laminate film. It is conductedto use such a non-volatile memory cell manufacturing process and form acapacitor element simultaneously with the memory cell. Moreparticularly, a lower electrode of the capacitor element is formed inthe process of forming the control gate electrode of the non-volatilememory cell and a capacitor insulating film of the capacitor element isformed in the process of forming a laminate film including a chargestorage film of the non-volatile memory. Further, an upper electrode ofthe capacitor element is formed in the process of forming the memorygate electrode of the non-volatile memory cell. In this way thecapacitor element can be formed in the non-volatile memory cell formingprocess and therefore the capacitor element can be formed on asemiconductor substrate without the addition of any new process forforming the capacitor element. Thus, even if the capacitor element isformed on the semiconductor substrate, it is possible to prevent a risein manufacturing cost of the semiconductor device. This capacitorelement is called PIP (Polysilicon Insulator Polysilicon) capacitorelement because a polysilicon film is used for each of upper and lowerelectrodes.

For example, as noted above, since the PIP capacitor element is used fora booster circuit or an analog circuit, a relatively high voltage isapplied to the upper and lower electrodes as components of the PIPcapacitor element. Therefore, the PIP capacitor element is required tobe high in reliability so as to operate normally with high accuracy evenwhen a high voltage is applied thereto.

FIG. 25 is a plan view showing a PIP capacitor element C which thepresent inventors have studied. As shown in the same figure, a lowerelectrode 109 and an upper electrode 110 have respective rectangularshapes different from each other and have a mutually planarlyoverlapping region and planarly non-overlapping regions. That is, inFIG. 25, the length of the lower electrode 109 is larger than that ofthe upper electrode 110 in x direction, while in y direction the lengthof the lower electrode 109 is smaller than that of the upper electrode110. The PIP capacitor element C is formed in the planarly overlappingregion of both upper and lower electrodes 109, 110. In thenon-overlapping regions of the lower electrode 109 there are formedplugs 114 coupled electrically to the lower electrode 109. Likewise, inthe non-overlapping regions of the upper electrode 110 there are formedplugs 115 coupled electrically to the upper electrode 110. By formingthe plugs 115 coupled to the upper electrode 110 in the non-overlappingregion of the upper electrode 110 it is possible to improve thereliability of the PIP capacitor element C. For example, in the case ofa shape in which the upper electrode is planarly included in the lowerelectrode, there exists only a planarly overlapping region between theupper and lower electrodes. It follows that the plugs coupledelectrically to the upper electrode are formed on the overlappingregion. That is, the plugs coupled to the upper electrode are formed onthe PIP capacitor element formed in the overlapping region. In thiscase, formation of the plugs coupled to the upper electrode may resultin damage to a capacitor insulating film which is in contact with thebottoms of the plugs. Since the capacitor insulating film possesses animportant role in the characteristics of the PIP capacitor element,damage thereof would lead to deterioration in characteristics of the PIPcapacitor element.

To avoid such an inconvenience, as shown in FIG. 25, the upper electrode110 and the lower electrode 109 are formed in different rectangularshapes to permit formation of both overlapping region andnon-overlapping regions. The overlapping region serves as the PIPcapacitor element C and the non-overlapping regions of the upperelectrode 110 serve as lead-out regions of the upper electrode 110. Byforming the plugs 115 coupled to the upper electrode 110 in the lead-outregions formed in the non-overlapping regions it is possible to preventdamage to the capacitor insulating film of the PIP capacitor element Cformed in the overlapping region. That is, since the PIP capacitorelement C is not formed in the non-overlapping regions (lead-outregions) of the upper electrode 110, there arises no problem incharacteristics of the PIP capacitor element even if the plugs 115 areformed in the non-overlapping regions. For this reason there is usedsuch a PIP capacitor element C as shown in FIG. 25 which is of astructure having an overlapping region and non-overlapping regions.

With this PIP capacitor element C, however, the following problem isbeing actualized. A description will be given about this problem. FIG.26 is a sectional view taken on line A-A in FIG. 25. As shown in thesame figure, an element isolation region 101 is formed in asemiconductor substrate 100 and a PIP capacitor element is formed on theelement isolation region 101. More specifically, a lower electrode 109is formed on the element isolation region 101 and a capacitor insulatingfilm 106 comprised of a silicon oxide film 103, a silicon nitride film104 and a silicon oxide film 105 is formed on the lower electrode 109,further, an upper electrode 110 is formed on the capacitor insulatingfilm 106. The PIP capacitor element thus comprised of the lowerelectrode 109, the capacitor insulating film 106 and the upper electrode110 is covered with an insulating film 113 which serves an interlayerinsulating film, and there are formed plugs 114 extending through theinsulating film 113 and reaching the lower electrode 109. The plugs 114are formed in non-overlapping regions of the lower electrode 109.

The lower electrode 109 is comprised of a polysilicon film 102 and ametal silicide film (e.g., cobalt silicide film) 108 formed on a surfaceof the polysilicon film 102. The metal silicide film 108 is formed inregions not planarly overlapping the upper electrode 110. Further, sidewalls 112 comprised of an insulating film is formed at end portions ofthe lower electrode 109.

The upper electrode 110 is comprised of a polysilicon film 107 and ametal silicide film (e.g., cobalt silicide film) 108 formed on a surfaceof the polysilicon film 107. Further, side walls 111 are formed at endportions of the upper electrode 110.

The metal silicide film 108 can be formed on the surface of thepolysilicon film 107 as a constituent of the upper electrode 110 andalso on the surface of the polysilicon film 102 as a constituent of thelower electrode 109 by depositing a metal film in contact with thepolysilicon films 107 and 102 which are exposed and subsequent heattreatment, allowing a silicide reaction to take place between the metalfilm and the polysilicon film 107 (102). At this time, the metalsilicide film may grow to an abnormal extent. Particularly, if the metalsilicide film 108 grows to an abnormal extent at end portions of theupper electrode 110, as shown in FIG. 26, the metal silicide film 108creeps up the side walls 111 from the end portions of the upperelectrode 110 and there occurs connection thereof with the metalsilicide film 108 formed on the surface of the lower electrode 109. As aresult, the upper electrode 110 and the lower electrode 109 are coupledtogether electrically through the metal silicide film 108, causing ashort-circuit defect. Upon occurrence of a short-circuit defect, the PIPcapacitor element no longer operates normally, thus giving rise to theproblem that the reliability of the PIP capacitor element isdeteriorated. Particularly, as the polysilicon film 107 as a constituentof the upper electrode 110 becomes thin and the distance between thelower electrode 109 and the upper electrode 110 becomes short, theshort-circuit defect caused by the abnormal growth of the metal silicidefilm 108 becomes conspicuous.

There sometimes is a case where the PIP capacitor element formed on thesemiconductor substrate is manufactured by an independent manufacturingprocess, but usually, for simplification of the semiconductor devicemanufacturing process, the PIP capacitor element is formed in theprocess of forming a non-volatile memory cell.

Recently, the non-volatile memory cell formed in the same process as thePIP capacitor element has been becoming more and more fine. This meansthat the gate length of a gate electrode (especially a memory gateelectrode) of the non-volatile memory cell becomes smaller. Formicrominiaturizing the gate length of the memory gate electrode, thethickness of the polysilicon film which configures the memory gateelectrode tends to become smaller. That is, the memory gate electrode isformed on each side wall of a control gate electrode, but for shorteningthe gate length of the memory gate electrode it is necessary to thin thepolysilicon film which is formed so as to cover the control gateelectrode. By forming the polysilicon film thin it is possible to narrowthe width of the memory gate electrode which is formed on each side wallof the control gate electrode by anisotropic etching. More particularly,the width of the memory gate electrode formed on each side wall of thecontrol gate electrode depends on the thickness of deposited polysiliconfilm. This means that the thinner the thickness of the polysilicon filmwhich configures the memory gate electrode, the thinner the film of theupper electrode as a constituent of the PIP capacitor element. This isbecause the upper electrode as a constituent of the PIP capacitorelement is formed by the same film as the polysilicon film whichconfigures the memory gate electrode.

Accordingly, with respect to the PIP capacitor element formed in thesame process as the non-volatile memory cell, the polysilicon film whichconfigures the upper electrode is becoming more and more thin, andparticularly a short-circuit defect caused by abnormal growth of a metalsilicide film is becoming conspicuous as a problem. Thus, it is seenthat in the case of the PIP capacitor element including an overlappingregion and non-overlapping regions as upper electrode-forming regions, ashort-circuit defect caused by abnormal growth of a metal silicide filmposes a problem, and particularly in the case of the PIP capacitorelement formed in the same process as the non-volatile memory cell therearises a serious problem because the film thickness of the upperelectrode becomes smaller.

Further, in the PIP capacitor element including an overlapping regionand non-overlapping regions as upper electrode-forming regions, therealso exists the following problem in addition to the above short-circuitproblem. FIG. 27 is a sectional view taken on line B-B in FIG. 25. Asshown in FIG. 27, an element isolation region 101 is formed in thesemiconductor substrate 100 and the PIP capacitor element is formed onthe element isolation region 101. The PIP capacitor element has a lowerelectrode 109 on the element isolation region 101 and a capacitorinsulating film 106 is formed so as to cover the lower electrode 109.The capacitor insulating film 106 is comprised of silicon oxide film103, silicon nitride film 104 and silicon oxide film 105. An upperelectrode 110 is formed on the capacitor insulating film 106. In thisB-B section, the length of the upper electrode 110 is larger than thatof the lower electrode 109, so that there occur stepped regions in theupper electrode 110. That is, in the upper electrode 110 there exist anoverlapping region which covers the lower electrode 109 as an underlyinglayer and non-overlapping regions (lead-out regions) free of anyunderlying lower electrode 109, thus inevitably creating stepped regionsbetween the overlapping region and the non-overlapping regions. Aninsulating film 113 serving as an interlayer insulating film is formedon the upper electrode 110 and plugs 115 are formed in the insulatingfilm 113, the plugs 115 extending through the insulating film 113 andreaching the upper electrode 110. The plugs 115 are coupled to thenon-overlapping regions of the upper electrode 110. Further, side walls112 are formed at end portions of the upper electrode 110 and side walls111 are formed also in the stepped regions which are formed in boundaryregions between the overlapping region and the non-overlapping regionsof the upper electrode 110.

As shown in FIG. 27, the upper electrode 110 is comprised of apolysilicon film 107 and a metal silicide film 108 formed on the surfaceof the polysilicon film 107. The metal silicide film 108 is formed bysiliciding the polysilicon film 107. This silicidation is promoted atupper end portions of the stepped regions (boundary regions between theoverlapping region and the non-overlapping regions) of the upperelectrode 110. This is for the following reason. The side walls 111 areformed on side walls of the stepped regions, but at the upper endportions of the stepped regions the side walls 111 are removed easilyand the polysilicon film is exposed. That is, at the upper end portionsof the stepped regions, silicidation proceeds in both horizontal andvertical directions and therefore the metal silicide film 108 becomesthicker in comparison with the other regions. Consequently, at the upperend portions of the stepped regions, the distance between the metalsilicide film 108 and the capacitor insulating film 106 becomes shortand the metal silicide film 108 becomes thick, so that fieldconcentration is apt to occur. Thus, at the upper end portions of thestepped regions, dielectric breakdown is apt to occur under theinfluence of the field concentration and the influence of the shorteneddistance between the metal silicide film 108 and he capacitor insulatingfilm 106. Once dielectric breakdown of the capacitor insulating film 106occurs, the PIP capacitor element does not operate normally, giving riseto the problem that the reliability of the PIP capacitor element isdeteriorated. This problem can also be considered to be become moremarked as the polysilicon film which configures the upper electrode 110becomes thinner, thus posing a serious problem for the PIP capacitorelement formed in the same process as the non-volatile memory cell.

It is an object of the present invention to provide a technique capableof improving the reliability of a capacitor element in a semiconductordevice including the capacitor element.

The above and other objects and novel features of the present inventionwill become apparent from the following description and the accompanyingdrawings.

The following is an outline of typical modes of the present invention asdisclosed herein.

A semiconductor device according to a typical mode of the presentinvention comprises (a) a semiconductor substrate, (b) an elementisolation region formed over the semiconductor substrate, and (c) acapacitor element formed over the element isolation region, thecapacitor element including (c1) a lower electrode formed over theelement isolation region, (c2) a capacitor insulating film formed overthe lower electrode and (c) an upper electrode formed over the capacitorinsulating film, wherein the length of the upper electrode in a firstdirection is larger than that of the lower electrode in the firstdirection, the length of the upper electrode in a second directionintersecting the first direction is smaller than that of the lowerelectrode in the second direction, the capacitor element is formed in aregion (overlapping region) where the upper electrode and the lowerelectrode overlap each other planarly, and over a surface of the upperelectrode there exist a region where a metal silicide film is formed anda region where the metal silicide film is not formed, the metal silicidefilm-formed region comprising a region spaced apart from end regions ofthe upper electrode in the second direction and a region spaced apartfrom stepped regions of the upper electrode in the first direction.

According to the above typical mode of the present invention, in theupper electrode, the regions where the metal silicide film is formed arelimited to the region spaced apart from end regions of the upperelectrode in the second direction and the region spaced apart fromstepped regions of the upper electrode in the first direction.Consequently, it is possible to suppress the occurrence of ashort-circuit defect caused by creeping-up of the metal silicide filmfrom end regions of the upper electrode and reaching the surface of thelower electrode and also possible to suppress dielectric breakdown ofthe capacitor insulating film caused by field concentration in steppedregions of the upper electrode.

A method for manufacturing a semiconductor device according to anothertypical mode of the present invention comprises the steps of (a) formingan element isolation region over a semiconductor substrate and (b)forming a capacitor element over the element isolation region, the step(b) including the steps of (b1) forming a lower electrode over theelement isolation region, (b2) forming a capacitor insulating film overthe lower electrode and (b3) forming an upper electrode over thecapacitor insulating film, the lower electrode and the upper electrodebeing formed in such a manner that the length of the upper electrode ina first direction is larger than that of the lower electrode in thefirst direction and the length of the upper electrode in a seconddirection intersecting the first direction is smaller than that of thelower electrode in the second direction, the capacitor element beingformed in an planarly overlapping region of the upper electrode and thelower electrode, the step (b) further including the steps of (b4), afterthe step (b3), forming an insulating film over the upper electrode, (b5)patterning the insulating film to cover with the insulating filmpredetermined regions including end regions of the upper electrode inthe second direction and predetermined regions including stepped regionsof the upper electrode in the first direction, and then (b6), after thestep (b5), forming a metal silicide film over a surface of the upperelectrode, the metal silicide film formed over the surface of the upperelectrode being formed in a region spaced apart from the end regions ofthe upper electrode in the second direction and also formed in a regionspaced apart from the stepped regions of the upper electrode in thefirst direction.

Thus, according to another typical mode of the present invention, in theupper electrode, a metal silicide film is not formed in end regions ofthe upper electrode in the second direction and stepped regions of theupper electrode in the first direction. Therefore, it is possible tosuppress the occurrence of a short-circuit defect caused by creeping-upof the metal silicide film from the end regions of the upper electrodeand also suppress the occurrence of dielectric breakdown of thecapacitor insulating film caused by field concentration in the steppedregions of the upper electrode.

The following is a brief description of effect obtained by the typicalmodes of the present invention as disclosed herein.

According to the above typical modes of the present invention, in thePIP capacitor element wherein the upper electrode-forming regionincludes an overlapping region overlapping with the lower electrodeplanarly and non-overlapping regions not overlapping with the lowerelectrode, the regions of the metal silicide film formed over the upperelectrode are limited to a region spaced apart from end regions of theupper electrode and a region spaced apart from stepped regions of theupper electrode. Consequently, it is possible to suppress the occurrenceof a short-circuit defect caused by creeping up of the metal silicidefilm from end regions of the upper electrode and reaching the surface ofthe lower electrode and also possible to suppress dielectric breakdownof the capacitor insulating film caused by field concentration atstepped regions of the upper electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a layout configuration of a semiconductorchip;

FIG. 2 is a plan view showing the configuration of a capacitor elementin a first embodiment of the present invention;

FIG. 3 is a sectional view taken on line A-A in FIG. 2;

FIG. 4 is a sectional view taken on line B-B in FIG. 2;

FIG. 5 is a plan view showing a feature of the capacitor element in thefirst embodiment;

FIG. 6 is a sectional view showing the configuration of a memory celland that of the capacitor element in the first embodiment;

FIG. 7 is a sectional view showing a semiconductor device manufacturingprocess in the first embodiment;

FIG. 8 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 7;

FIG. 9 is a sectional view showing the semiconductor device manufactureprocess in a step which follows FIG. 8;

FIG. 10 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 9;

FIG. 11 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 10;

FIG. 12 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 11;

FIG. 13 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 12;

FIG. 14 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 13;

FIG. 15 is a sectional view showing the semiconductor manufacturingprocess in a step which follows FIG. 14;

FIG. 16 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 15;

FIG. 17 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 16;

FIG. 18 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 17;

FIG. 19 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 18;

FIG. 20 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 19;

FIG. 21 is a sectional view showing the semiconductor devicemanufacturing process in a step which follows FIG. 20;

FIG. 22 is a plan view showing the configuration of a capacitor elementin a second embodiment of the present invention;

FIG. 23 is a sectional view showing the configuration of a capacitorelement in a third embodiment of the present invention;

FIG. 24 is a sectional view showing the configuration of the capacitorelement in the third embodiment;

FIG. 25 is a plan view showing the configuration of a capacitor elementwhich the present inventors have studied;

FIG. 26 is a sectional view taken on line A-A in FIG. 25; and

FIG. 27 is a sectional view taken on line B-B in FIG. 25.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following embodiments will each be described dividedly into pluralsections or embodiments where required for the sake of convenience, butunless otherwise mentioned, they are not unrelated to each other, butone is in a relation of modification or detailed or supplementaryexplanation of part or the whole of the other.

When reference is made to, for example, the number of elements(including the number of pieces, numerical value, quantity, and range)in the following embodiments, no limitation is made to the specifiednumber, but numbers above and below the specified number will do unlessotherwise mentioned and except the case where limitation is made to thespecified number basically clearly.

In the following embodiments, moreover, it goes without saying thattheir constituent elements (including constituent steps) are not alwaysessential unless otherwise mentioned and except the case where they areconsidered essential basically clearly.

Likewise, in the following embodiments, it is to be understood that whenreference is made to the shape and positional relation of a constituentelement, those substantially similar or closely similar thereto are alsoincluded unless otherwise mentioned and except the case where the answeris negative basically clearly. This is also true of the foregoingnumerical value and range.

In all of the drawings for illustrating the embodiments, the sameportions are identified by the same reference numerals, and repeatedexplanations thereof will be omitted, in principle. Even plan views maybe hatched to make them easier to see.

First Embodiment

FIG. 1 is a plan view showing a semiconductor chip (semiconductorsubstrate) CHP with a microcomputer formed thereon for example. A layoutconfiguration of elements formed on the semiconductor chip CHP is shownin the same figure. In FIG. 1, the semiconductor chip CHP includes a CPU(Central Processing Unit) 1, a RAM (Random Access Memory) 2, an analogcircuit 3 and a flash memory 4. In the peripheral portion of thesemiconductor chip there are formed pads PD as external terminals forinput and output to provide coupling between the above circuits andexternal circuits.

The CPU (circuit)) 1, which is also called central processing unit,corresponds to the nucleus of a computer. The CPU 1 reads instructionsfrom a storage device, then decodes them and performs variouscalculations and controls on the basis of the decoded instructions. TheCPU 1 is required to be high in processing speed. Therefore, it isconsidered that a relatively larger current drive force is required ofthe MISFET (Metal Insulator Semiconductor Field Effect Transistor) amongthe elements formed in the semiconductor chip CHP. That is, the MISFETis a low voltage-proof MISFET.

The RAM (circuit)) 2 is a memory which can read stored informationrandomly, or at any time, and newly write information. It is also calleda random access memory. There are two types of RAMs as IC memories,which are DRAM (Dynamic RAM) using a dynamic circuit and SRAM (StaticRAM) using a static circuit. DRAM is a random access memory requiring astorage holding operation, while SRAM is a random access memory notrequiring a storage holding operation. Since the RAM 2 is also requiredto be high in operation speed, it is considered that a relatively largecurrent drive force is required of the MISFET which configures the RAM2. That is, the MISFET in question is a low voltage-proof MISFET.

The analog circuit 3 is a circuit which handles timewise continuouslychanging voltage and current signals, i.e., analog signals, and forexample it is comprised of an amplifier circuit, a converter circuit, amodulator circuit, an oscillator circuit and a power supply circuit. Asthe analog circuit 3 there is used a relatively high voltage-proofMISFET among the elements formed in the semiconductor chip CHP.

The flash memory 4 is a kind of non-volatile memory permittingelectrical rewrite of both write and erase operations. It is also calledan electrically erasable programmable read-only memory. The memory cellof the flash memory 4 is comprised of MISFET for memory selection andfor example a MONOS (Metal Oxide Nitride Oxide Semiconductor) type FETfor memory. For write operation of the flash memory there is utilized,for example, hot electron injection or Fowler-Nordheim tunnel phenomenonand for erase operation of the flash memory there is utilizedFowler-Nordheim tunnel phenomenon or hot hole injection. It goes withoutsaying that the hot electron injection and the hot hole injection may bereversed.

A drive circuit such as a booster circuit is formed in the semiconductorchip for operating the flash memory described above. A highly accuratecapacitor element is required of the drive circuit. Also for the analogcircuit 3 described above, a highly accurate capacitor element isrequired. Thus, not only the flash memory 4, memory cells and MISFETs,but also a capacitor element is formed in the semiconductor chip CHP. Inthis first embodiment, one feature resides in the capacitor elementformed in the semiconductor chip CHP. The following description isprovided about the configuration of the capacitor element formed in thesemiconductor chip CHP.

FIG. 2 is a plan view showing a PIP capacitor element C used in thisfirst embodiment. As shown in the same figure, a lower electrode 16 andan upper electrode 23 are of rectangular shapes different from eachother, having a planarly overlapping region of both lower and upperelectrodes 16, 23 and planarly non-overlapping regions of the two. Morespecifically, as shown in FIG. 2, the length of the lower electrode 16is larger than that of the upper electrode 23 in x direction, while in ydirection (direction intersecting the x direction) the length of thelower electrode 16 is smaller than that of the upper electrode 23. ThePIP capacitor element C is formed in the planarly overlapping region ofthe lower and upper electrodes 16, 23. Plugs 37 b coupled electricallyto the lower electrode 16 are formed in the non-overlapping regions ofthe lower electrode 16, while plugs 37 c coupled electrically to theupper electrode 23 are formed in the non-overlapping regions of theupper electrode 23. The plugs 37 b coupled electrically to the lowerelectrode 16 are coupled to wiring lines HL2, while the plugs 37 ccoupled electrically to the upper electrode 23 are coupled to wiringlines HL3. By forming the plugs 37 c coupled to the upper electrode 23in the non-overlapping regions of the upper electrode 23 it is possibleto improve the reliability of the PIP capacitor element.

For example, in the case of a shape wherein the upper electrode isincluded in the lower electrode planarly, there exists only a planarlyoverlapping region between the upper and lower electrodes. It followsthat the plugs coupled electrically to the upper electrode are formed onthe overlapping region. That is, the plugs coupled to the upperelectrode are formed on the PIP capacitor element formed in theoverlapping region. In this case, if the plugs coupled to the upperelectrode are formed, there is a fear of damage to a capacitorinsulating film which is in contact with the bottoms of the plugs. Sincethe capacitor insulating film plays an important role in thecharacteristics of the PIP capacitor element, damage of the capacitorinsulating film would lead to deterioration in characteristics of thePIP capacitor element.

To avoid this inconvenient, as shown in FIG. 2, the upper electrode 23and the lower electrode 16 are formed in different rectangular shapes toprovide an overlapping region and non-overlapping regions. Theoverlapping region serves as the PIP capacitor element, while thenon-overlapping regions of the upper electrode 23 serve as lead-outregions of the upper electrode 23. By forming the plugs 37 c coupled tothe upper electrode 23 in the lead-out regions formed non-overlappingregions it is possible to prevent damage to the capacitor insulatingfilm of the PIP capacitor element formed in the overlapping region.Since the PIP capacitor element C is not formed in the non-overlappingregions (lead-out regions) of the upper electrode 23, even if the plugs37 c are formed in the non-overlapping regions, there is no problem inpoint of characteristics of the PIP capacitor element. For this reasonthere is used the PIP capacitor element C of a structure having bothoverlapping region and non-overlapping regions as in FIG. 2. With thePIP capacitor element C of such a structure as a premise, features ofthe PIP capacitor element C in this first embodiment will be describedbelow with reference to a sectional view.

FIG. 3 is a sectional view taken on line A-A in FIG. 2. As shown in FIG.3, an element isolation region 11 is formed on a semiconductor substrate10 made of a single silicon crystal for example and a PIP capacitorelement is formed on the element isolation region 11. The PIP capacitorelement includes a lower electrode 16 formed on the element isolationregion. The lower electrode 16 is comprised of a polysilicon film 14 anda cobalt silicide film 33 formed on a surface of the polysilicon film14. A capacitor insulating film 27 having a length shorter in xdirection (lateral direction in FIG. 3) than the lower electrode 16 isformed on the lower electrode 16. For example, the capacitor insulatingfilm 27 is comprised of a laminate of silicon oxide film, siliconnitride film and silicon oxide film. An upper electrode 23 is formed onthe capacitor insulating film 27. The upper electrode 23 is comprised ofa polysilicon film 20 and a cobalt silicide film 33 formed on a surfaceof the polysilicon film 20.

Then, side walls 29 b are formed on side walls respectively of the upperelectrode 27 and the capacitor insulating film 27 and side walls 29 care formed on side walls of the lower electrode 16. The side walls 29 bformed on the side walls of the upper electrode 23 and the capacitorinsulating film 27 function to improve the insulation between the upperelectrode 23 and the lower electrode 16.

In the A-A section of FIG. 2, which is shown in FIG. 3, the length ofthe lower electrode 16 is larger than that of the upper electrode 23, sothat, as shown in FIG. 3, in the region where the lower electrode 16 isformed there exist an overlapping region overlapping with the upperelectrode 23 and non-overlapping regions where the upper electrode 23 isnot formed over the lower electrode 16. Therefore, the PIP capacitorelement is formed in the overlapping region where the lower electrode 16and the upper electrode 23 overlap each other planarly. On the otherhand, a cobalt silicide film is formed in each of the non-overlappingregions of the lower electrode 16 and plugs 37 b are formed on thecobalt silicide film 33, the plugs 37 b extending through an interlayinginsulating film 34 and being coupled to the lower electrode 16electrically. The plugs 37 b are coupled to wiring lines HL2 formed onthe interlayer insulating film 34. The cobalt silicide film 33 formed onthe non-overlapping regions of the lower electrode 16 are for making thelower electrode 16 low in resistance. The cobalt silicide film 33 isformed also on a surface of the upper electrode 23, whereby the upperelectrode 23 is made low in resistance. Therefore, it can be saiddesirable from the standpoint of making the upper electrode 23 and thelower electrode 16 low in resistance that the cobalt silicide film 33formed on the surface of the upper electrode 23 and the cobalt silicidefilm 33 formed on the non-overlapping regions of the lower electrode 16be formed in as large regions as possible.

However, for example, if the cobalt silicide film is formed throughoutthe whole surface of the upper electrode, it is formed even at planarboundaries (end portions of the upper electrode 23) between the upperelectrode 23 and the lower electrode 16. In this case, if the cobaltsilicide film 33 grows abnormally in the siliciding process for formingthe cobalt silicide film 33, the cobalt silicide film 33 is formed whilecreeping up along the side walls 29 b from end portions of the upperelectrode 23. The cobalt silicide film 33 thus formed while creeping upalong the side walls 29 b is coupled to the cobalt silicide film 33formed in the non-overlapping regions of the lower electrode 16. As aresult, the upper electrode 23 and the lower electrode 16 are renderedconductive by the cobalt silicide film 33 and the PIP capacitor elementno longer operates normally.

To avoid such an inconvenience, as shown in FIG. 3, one feature of thisfirst embodiment resides in that the cobalt silicide film 33 is notformed throughout the whole surface of the upper electrode 23, but isformed in an inner region spaced apart a distance L1 from each endportion of the upper electrode 23. That is, the cobalt silicide film 33is formed in only a region spaced apart from end regions of the upperelectrode 23. In other words, the cobalt silicide film 33 is not formedin regions closer than L1 as the distance from each end region of theupper electrode 23. By so doing it is possible to prevent the cobaltsilicide film 33 from growing abnormally while creeping along the sidewalls 29 b from end portions of the upper electrode 23. Thus, in thisfirst embodiment, end portions of the cobalt silicide film 33 formed onthe surface of the upper electrode 23 lie inside spaced apart from endportions of the upper electrode 23. That is, the cobalt silicide film 33is not present at end portions of the upper electrode 23, thus making itpossible to prevent abnormal growth of the cobalt silicide film 33.

This first embodiment is characteristic in that the cobalt silicide film33 is not formed at end portions of the upper electrode 23. In otherwords, the cobalt silicide film 33 is spaced apart from the side walls29 b formed at end portions of the upper electrode 23. Consequently, itis possible to prevent the cobalt silicide film 33 from creeping outfrom end portions of the upper electrode 23 toward the side walls 29 b.In this embodiment the cobalt silicide film 33 is formed so as to bespaced apart the distance L1 from each end portion of the upperelectrode 23. The distance L1 is a sufficient distance for preventingthe cobalt silicide film 33 from creeping out to the side walls 29 b.Even if the distance L1 is short, it is possible to prevent the cobaltsilicide film 33 from creeping up to the side walls 29 b in comparisonwith the case where the cobalt silicide film 33 is formed up to endportions of the upper electrode 23. That is, the distance L1 indicatesthat an end portion of the cobalt silicide film 33 is spaced apart fromthe upper electrode 23. As long as this separation is ensured, even ifthe distance L1 is short, it is possible to prevent the occurrence of ashort-circuit defect between the upper electrode 23 and the lowerelectrode 16 caused by abnormal growth of the cobalt silicide film 33.

A concrete description will now be given about an optimum distance L1.The cobalt silicide film 33 is formed on the upper electrode 23 in thefollowing manner. Cobalt film is deposited on the upper electrode 23comprised of the polysilicon film 20, followed by heat treatment,whereby there occurs a silicidation reaction between the polysiliconfilm 20 and the cobalt film and the cobalt silicide film 33 is formed onthe surface of the polysilicon film. At this time, if the thickness ofthe cobalt film deposited on the polysilicon film 20 is set at about 10nm for example, the thickness of the cobalt silicide film formed isabout 20 nm. Therefore, by setting the distance L1 at about 20 nm it ispossible to prevent the cobalt silicide film 33 from reaching endportions of the upper electrode 23. That is, by setting the distance L1from an end portion of the cobalt silicide from 33 to an end portion ofthe upper electrode 23 it is possible to effectively prevent the cobaltsilicide film from creeping out to the side walls 29 b from end portionsof the upper electrode 23. However, the distance L1 of 20 nm is a valuetaken when the deposition thickness of the cobalt film is about 10 nmand the value of the distance L1 can vary depending on the depositionthickness of the cobalt film and the thickness of the cobalt silicidefilm 33 formed. Although a concrete numerical example of the distance L1has been shown, the features of this first embodiment are not limitedthereto insofar as end portions of the cobalt silicide film 33 arespaced apart from end portions of the upper electrode 23. Particularly,if the distance L1 from the upper electrode 23 is approximately equal tothe thickness of the cobalt silicide film, it is possible to fullyprevent the occurrence of a short-circuit defect between the upperelectrode 23 and the lower electrode 16 caused by abnormal growth of thecobalt silicide film 33.

A description will now be given a further characteristic configurationwhich can diminish a short-circuit defect between the upper electrode 23and the lower electrode 16 caused by abnormal growth of the cobaltsilicide film 33. As shown in FIG. 3, another feature of this firstembodiment resides in that the cobalt silicide film 33 formed on asurface of the lower electrode 16 is also spaced apart from boundaries(stepped regions) between the upper electrode 23 and the lower electrode16. More specifically, the cobalt silicide film 33 is formed on thelower electrode 16 so as to be spaced apart from the side walls 29 bformed at the boundaries (stepped regions) between the upper electrode23 and the lower electrode 16. By so doing, even if the cobalt silicidefilm 33 creeps out along surfaces of the side walls 29 b from the upperelectrode 23, it is possible to prevent the creeping cobalt silicidefilm from joining the cobalt silicide film formed on the lower electrode16. As a result, it is possible to diminish the occurrence of ashort-circuit defect between the upper electrode 23 and the lowerelectrode 16.

For example, in the case where the cobalt silicide film 33 formed on thesurface of the lower electrode 16 is put in contact with the side walls29 b, the cobalt silicide film 33 creeping out from end portions of theupper electrode 23 to the side walls 29 b becomes easier to contact thecobalt silicide film 33 formed on the surface of the lower electrode 16.On the other hand, by spacing the cobalt silicide film 33 formed on thelower electrode 16 apart from the side walls 29 b it is possible toprevent an electrical coupling between the cobalt silicide film creepingout from end portions of the upper electrode 23 to the side walls 29 band the cobalt silicide film 33 formed on the lower electrode 16. Thatis, by forming the cobalt silicide film 33 on the lower electrode 16 soas to be spaced apart the distance L2 from the boundaries (steppedregions) between the upper electrode 23 and the lower electrode 16 it ispossible to diminish the occurrence of a short-circuit defect betweenthe upper electrode 23 and the lower electrode 16.

A concrete description will now be given about an optimum distance L2.For example, if the thickness of the cobalt film deposited on thepolysilicon film 14 is assumed to be about 10 nm, the thickness of theresulting cobalt silicide film 33 is about 20 nm. Therefore, by settingthe distance L2 at about 20 nm, the cobalt silicide film 33 creeping outalong the side walls 29 b can be prevented from contacting the cobaltsilicide film 33 formed on the lower electrode 16. That is, by spacingend portions of the cobalt silicide film 33 on the lower electrode 16about 20 nm apart from the boundaries between the upper electrode 23 andthe lower electrode 16 it is possible to effectively prevent anelectrical contact between the cobalt silicide film 33 creeping outalong the side walls 29 b from end portions of the upper electrode 23and the cobalt silicide film 33 formed on the lower electrode 16.However, the distance L2 of 20 nm is a value taken when the depositionthickness of the cobalt film is about 10 nm and the value of L2 can varydepending on the deposition thickness of the cobalt film and thethickness of the cobalt silicide film 33 formed. Although a concretenumerical example of the distance L2 has been described, the features ofthis first embodiment are not limited thereto insofar as end portions ofthe cobalt silicide film 33 formed on the lower electrode 16 are spacedapart from the boundaries between the upper electrode 23 and the lowerelectrode 16. Particularly, if the distance L2 from each boundary isapproximately equal to the thickness of cobalt silicide film, it ispossible to fully prevent the occurrence of a short-circuit defectbetween the upper electrode 23 and the lower electrode 16 caused byabnormal growth of the cobalt silicide film 33.

Thus, this first embodiment adopts two characteristic configurations forpreventing the occurrence of a short-circuit defect between the upperelectrode 23 and the lower electrode 16. The first feature resides inthat end portions of the cobalt silicide film 33 formed the upperelectrode 23 are spaced the distance L1 from end portions of the upperelectrode 23. According to this configuration it is possible to preventthe cobalt silicide film 33 from reaching end portions of the upperelectrode 23 and creeping out along the side walls 29 b. The secondfeature resides in that end portions of the cobalt silicide film 33formed on the lower electrode 16 are spaced the distance L2 from theboundaries between the upper electrode 23 and the lower electrode 16,namely, the point that the cobalt silicide film 33 formed on the lowerelectrode 16 is spaced apart from the side walls 29 b. This secondfeature plays a complementary role for the first feature. Moreparticularly, the first feature affords the effect that it is possibleto prevent the cobalt silicide film 33 from reaching end portions of theupper electrode 23 and creeping out to the side walls 29 b. According tothe second feature, the cobalt silicide film 33 formed on the lowerelectrode 16 is spaced apart from the side walls 29 b. Therefore, it ispossible to prevent contact between the cobalt silicide film 33 creepingout along the side walls 29 b and the cobalt silicide film 33 formed onthe lower electrode 16. Thus, in the PIP capacitor element of this firstembodiment, it is possible to effectively prevent the occurrence of ashort-circuit defect between the upper electrode 23 and the lowerelectrode 16 caused by abnormal growth of the cobalt silicide film 33.

The configuration (first feature) that end portions of the cobaltsilicide film 33 formed on the upper electrode 23 are spaced apart thedistance L1 from end portions of the upper electrode 23 and the secondconfiguration (second feature) that end portions of the cobalt silicidefilm 33 formed on the lower electrode 16 are spaced apart the distanceL2 from the boundaries between the upper electrode 23 and the lowerelectrode 16 can be implemented in the following manner. For example, asshown in FIG. 3, a silicon oxide film 31 as an insulating film is formedso as to cover the regions (regions within the upper electrode 23)inside of the distance L1 from end portions of the upper electrode 23and the regions (regions within the lower electrode 16) inside thedistance L2 from the boundaries between the upper electrode 23 and thelower electrode 16. Thereafter, with the silicon oxide film 31 thusformed, a cobalt silicide film 33 is formed. Thus, a direct contactbetween polysilicon film and cobalt film can be avoided in the regionswhere the silicon oxide film 31 was formed. Accordingly, it is possibleto avoid formation of the cobalt silicide film 33 in the regions(regions within the upper electrode 23) inside of the distance L1 fromend portions of the upper electrode 23 and also in the regions (regionswithin the lower electrode 16) inside of the distance L2 from theboundaries between the upper electrode 23 and the lower electrode 16.The insulating film used to inhibit formation of the cobalt silicidefilm is not limited to the silicon oxide film 31, but it may be anotherfilm, e.g., silicon nitride film.

Next, a description will be given about another problem which causesdeterioration in reliability of the PIP capacitor element in this firstembodiment, as well as means for solving the problem. In this firstembodiment the PIP capacitor element has a planarly overlapping regionbetween the upper electrode and the lower electrode and planarlynon-overlapping regions. The overlapping region is utilized as a regionfor forming the PIP capacitor element, while the non-overlapping regionsare utilized as lead-out regions coupled to plugs. In such configurationthere occur stepped portions between the overlapping region where theupper electrode is formed over the lower electrode through a capacitorinsulating film and the non-overlapping regions where the upperelectrode is formed over the element isolation region. That is, sincethe upper electrode extends over the overlapping region and thenon-overlapping regions, there occur stepped portions between theoverlapping region and the non-overlapping regions. In this firstembodiment a description will be given first about the problem resultingfrom formation of the stepped portions in the upper electrode and thenabout means for solving the problem.

FIG. 4 is a sectional view taken on line B-B in FIG. 2. As shown in FIG.4, an element isolation region 11 is formed in a semiconductor device 10and a PIP capacitor element is formed on the element isolation region11. The PIP capacitor element has a lower electrode 16 on the elementisolation region 11 and a capacitor insulting film 27 is formed so as tocover the lower electrode 16, with an upper electrode 23 being formed onthe capacitor insulating film 27. In this B-B section, the length of theupper electrode 23 is larger than that of the lower electrode 16, sothat stepped regions are formed in the upper electrode 23, as shown inFIG. 4. That is, in the upper electrode 23 there exist an overlappingregion where the lower electrode 16 lies as an underlying layer andnon-overlapping regions (lead-out regions) where the lower electrode 16does not lie as an underlying layer. There inevitably occur steppedregions between the overlapping region and the non-overlapping regions.An interlayer insulating film 34 is formed on the upper electrode 23 andplugs 37 c are formed in the interlayer insulating film 34, the plugs 37c extending through the interlayer insulating film 34 and reaching theupper electrode 23. The plugs 37 c are formed so as to be coupled to thenon-overlapping regions of the upper electrode 23. Further, side walls29 e are formed at end portions of the upper electrode 23 and side walls29 d are also formed in stepped regions formed between the overlappingregion and the non-overlapping regions of the upper electrode 23.

As shown in FIG. 4, the upper electrode 23 is comprised of a polysiliconfilm 20 and a cobalt silicide film 33 formed on a surface of thepolysilicon film 20. The cobalt silicide film 33 is formed bysilicidation of the polysilicon film 20. The silicidation is acceleratedat upper end portions of the stepped regions (boundary regions betweenthe overlapping region and the non-overlapping regions) of the upperelectrode 23. The reason is that side walls 29 d are formed on sidewalls of the stepped regions, but at the upper end portions of thestepped regions the side walls 29 d are easily removed and thepolysilicon film 20 is exposed. That is, at the upper end portions ofthe stepped regions, the silicidation proceeds in both horizontal andvertical directions, so that the thickness of the cobalt silicide film33 tends to becomes larger than that of the other regions. Consequently,at the upper end portions of the stepped regions, the distance betweenthe cobalt silicide film 33 and the capacitor insulating film 27 becomesshort and the thickness of the cobalt silicide film 33 becomes larger,so that field concentration is apt to occur. Thus, at the upper endportions of the stepped regions, dielectric breakdown of the capacitorinsulating film 27 is apt to occur under the influence of fieldconcentration and also under the influence of a shorter distance betweenthe cobalt silicide film 33 and the capacitor insulating film 27. Oncedielectric breakdown of the capacitor insulating film 27 occurs, the PIPcapacitor element fails to operate normally and there arises the problemthat the reliability of the PIP capacitor element is deteriorated. Thisproblem inevitably arises from the configuration including steppedregions in the upper electrode and is peculiar to the PIP capacitorelement in this first embodiment.

In this first embodiment, to solve the above-mentioned problem, asilicon oxide film 31 as an insulating film is formed in each of regionslocated within a predetermine range from the stepped regions, whereby itis possible to prevent the cobalt silicide film 33 from being formed inregions located within the predetermined range from the stepped regions.More specifically, the cobalt silicide film 33 is not formed within therange of distance L3 from each stepped region of the upper electrode 23toward the overlapping region and also within the range of distance L4from each stepped region toward the associated non-overlapping region(side wall 29 d-formed region). That is, the silicon oxide film 31 isformed so as to cover the regions within the range of distance L3 fromthe stepped regions toward the overlapping region and also cover theregions within the range of distance L4 from the stepped regions towardthe non-overlapping regions (side-walls 29 d-formed regions).Consequently, the cobalt silicide film 33 formed on the surface of theupper electrode 23 is spaced apart from the stepped regions which arepresent in the boundary regions between the overlapping region and thenon-overlapping regions. Thus, the upper end portions of the steppedregions are covered with the silicon oxide film 31 and are not formedwith cobalt silicide film 33, so there is no fear that the silicidationmay proceed in both horizontal and vertical direction. Since the cobaltsilicide film 33 is thus not formed at the upper end portions of thestepped regions, it is possible to eliminate the influence of fieldconcentration in the stepped regions and the influence of shorterdistance between the cobalt silicide film 33 and the capaciatorinsulating film 27. Consequently, in the PIP capacitor element accordingto this first embodiment, it is possible to prevent dielectric breakdownof the capacitor insulating film 27 and improve the reliability of thecapacitor features.

A concrete description will now be given about an optimum distance L3.If the thickness of the cobalt film deposited on the polysilicon film 20is assumed to be about 10 nm, the thickness of the cobalt silicide film33 formed is bout 20 nm. Therefore, by setting the distance L3 at about20 nm, there is no fear of the cobalt silicide film 33 extending up theupper end portions of the stepped regions. That is, by spacing endportions of the cobalt silicide film 33 formed in the overlapping regionof the upper electrode 23 about 20 nm apart from the boundaries of thestepped regions, it is possible to effectively prevent formation of thecobalt silicide film 33 at the upper end portions of the steppedregions. However, the distance L3 of 20 nm is a value taken when thedeposition thickness of the cobalt film is about 10 nm and it can varydepending on the deposition thickness of the cobalt film and thethickness of the cobalt silicide film 33 formed. Although a concretenumerical example of the distance L3 has been shown, the features ofthis first embodiment are not limited thereto insofar as end portions ofthe cobalt silicide film 33 formed in the overlapping region of theupper electrode 23 are spaced apart from the stepped regions.Particularly, if the distance L3 from the stepped regions isapproximately equal to the thickness of the cobalt silicide film, it ispossible to fully prevent formation of the cobalt silicide film in thestepped regions.

Further, a description will be given about an optimum distance L4. Fromthe standpoint that the cobalt silicide film 33 is not formed at theupper end portions of the stepped regions, it suffices for the distanceL4 to be a distance at which the upper end portion of each steppedregion includes an exposed region. That is, it suffices for the distanceL4 to be a distance which covers from the boundary of each steppedregion up to near the region where the associated side wall 29 d isformed. However, in the first embodiment illustrated in FIG. 4, thedistance L4 extends from the boundary of the stepped region up to aregion spaced apart from the side wall 29 d beyond the same wall. Thisis done in consideration of misalignment which occurs in aphotolithography technique. According to the photolithography technique,the silicon oxide film 31 is formed so as to cover regions within therange of distance L from the stepped regions toward the overlappingregion and regions within the range of distance L4 from the steppedregions toward the non-overlapping regions (side walls 29 d-formedregions). That is, it is intended to prevent the stepped regions frombeing uncovered with the silicon oxide film 31 and left exposed bymisalignment in the photolithography technique. Therefore, it ispreferable that the distance L4 be equal to or larger than the thicknessof the upper electrode 24.

Features of the PIP capacitor element in this first embodiment will besummarized as follows. First, in the PIP capacitor element in this firstembodiment it is an important object to improve the reliability ofcapacitor characteristics. There are two concrete objects for achievingthe important object. One object is to remedy the short-circuit defectbetween the upper electrode and the lower electrode caused by abnormalgrowth of the cobalt silicide film and thereby improve the reliability.To achieve this object, as shown in FIG. 3, end portions of the cobaltsilicide film 33 formed on the upper electrode 23 are spaced apart thedistance L1 from end portions of the upper electrode 23, whereby it ispossible to prevent the cobalt silicide film 33 from reaching endportions of the upper electrode 23 and creeping out to the side walls 29b. Besides, end portions of the cobalt silicide film 33 formed on thelower electrode 16 are spaced apart the distance L2 from the boundariesbetween the upper electrode 23 and the lower electrode 16. According tothis configuration, even if the cobalt silicide film 33 grows abnormallyand creeps out to the side walls 29 b, the cobalt silicide film 33formed on the lower electrode 16 is spaced apart from the side walls 29b. Thus, there is obtained an effect that it is possible to preventcontact between the cobalt silicide film 33 creeping out along the sidewalls 29 b and the cobalt silicide film 33 formed on the lower electrode16.

Another object is to prevent dielectric breakdown of the capacitorinsulating film and thereby improve the reliability. To achieve thisobject, as shown in FIG. 4, the cobalt silicide film 33 is formedneither within the range of distance L3 from the stepped regions formedin the upper electrode 23 toward the overlapping region nor within therange of distance L4 from the stepped regions toward the non-overlappingregions (side walls 29 d-formed regions). Since the cobalt silicide film33 is not formed at the upper end portions of the stepped regions, it ispossible to eliminate the influence of field concentration in thestepped regions and the influence of a shorter distance between thecobalt silicide film 33 and the capacitor insulating film 27. Thus, inthe PIP capacitor element according to this first embodiment, it ispossible to prevent dielectric breakdown of the capacitor element 27 andimprove the reliability of the capacitor characteristics.

FIG. 5 is a plan view showing a characteristic configuration of thisfirst embodiment. In the same figure there are illustrated hatchedregions defined by distances L1 and L2 in the boundary regions betweenthe upper electrode 23 and the lower electrode 16. Further, hatchedregions defined by distances L3+L4 are illustrated in the boundaryregions (stepped regions) between the overlapping region and thenon-overlapping regions of the upper electrode 23. It is a feature ofthis first embodiment that the cobalt silicide film is not formed inthose hatched regions. According to this feature it is possible toprevent the occurrence of a short-circuit defect caused by creeping upof the cobalt silicide film from end regions of the upper electrode 23and reaching the surface of the lower electrode 16 and also preventdielectric breakdown of the capacitor insulating film caused by fieldconcentration in the stepped regions of the upper electrode 23. Althoughin connection with the PIP capacitor element according to this firstembodiment a description is being given about an example in which thecobalt silicide film as an example of the metal silicide film is formedon the surface of the upper electrode 23 and that of the lower electrode16, the technical idea in this first embodiment is applicable also tothe case where a titanium silicide film or a nickel silicide film isformed as the metal silicide film.

In this first embodiment, as described above, a feature resides in thestructure of the PIP capacitor element which is formed in thesemiconductor chip CHP shown in FIG. 1. Although the structure of thePIP capacitor element has been described above, there sometimes is acase where the PIP capacitor element is formed simultaneously in theprocess of forming a memory cell of the flash memory 4 as will bedescribed later. Therefore, a description will be given below whilemaking reference to illustrations about a memory cell of the flashmemory 4 formed in the semiconductor chip CHP and a PIP capacitorelement used in a drive circuit of the flash memory 4.

FIG. 6 is a sectional view showing the structure of a memory cell of theflash memory and that of a PIP capacitor element formed in the analogcircuit for example. In FIG. 6, the memory cell is formed in a memorycell-forming region (first region) of a semiconductor chip and the PIPcapacitor element is formed in a capacitor element-forming region(second region) of the semiconductor chip.

First, a description will be given about the structure of the memorycell of the flash memory. As shown in FIG. 6, in the memory cell-formingregion, a p-type well 12 is formed on a semiconductor substrate 10 and amemory cell is formed on the p-type well 12. This memory cell iscomprised of a select section for selecting the memory cell and astorage section for the storage of information. First, reference will bemade to the configuration of the select section for selecting a memorycell. The memory cell has a gate insulating film (first gate insulatingfilm) 13 formed on the semiconductor substrate 10 (p-type well 12), anda control gate electrode (control electrode) 15 is formed on the gateinsulating film 13. For example, the gate insulating film 13 is formedof a silicon oxide film and the control gate electrode 15 is comprisedof a polysilicon film 14 and a cobalt silicide film 33 formed on thepolysilicon film 14. The cobalt silicide film 33 is formed formed formaking the control gate electrode 15 low in resistance. The control gateelectrode 15 has a function of selecting a memory cell. That is, aspecific memory cell is selected by the control gate electrode 15 andwrite, erase or read operation is performed for the selected memorycell.

The following description is now provided about the configuration of thememory cell storage section. On one side wall of the control gateelectrode 15 is formed a memory gate electrode 26 through a laminate ofinsulating films. The memory gate electrode 26 is in the shape of a sidewall formed on one side wall of the control gate electrode 15 and iscomprised of a polysilicon film 20 and a cobalt silicide film 33 formedon the polysilicon film 20. The cobalt silicide film is formed formaking the memory gate electrode 26 low in resistance.

A laminate film is formed between the control gate electrode 15 and thememory gate electrode 26 and also between the memory gate electrode 26and the semiconductor substrate 10. The laminate film is comprised of asilicon oxide film (second gate insulating film) 17 formed on thesemiconductor substrate 10, a charge storage film 25 (silicon nitridefilm 18) formed on the silicon oxide film 17, and a silicon oxide film(first insulating film) 19 formed on the charge storage film 25. Thesilicon oxide film 17 functions as a gate insulating film formed betweenthe memory gate electrode 26 and the semiconductor substrate 10. Thisgate insulating film as the silicon oxide film 17 also has the functionas a tunnel insulating film. For example, since the memory cell storagesection inject electrons or holes from the semiconductor substrate 10into the charge storage film 25 through the silicon oxide film 17 tostore or erase information, the silicon oxide film 17 functions as atunnel insulating film.

The charge storage film 25 formed on the silicon oxide film functions tostore an electric charge. More specifically, in this first embodiment,the charge storage film 25 is formed of a silicon nitride film 18. Thememory cell storage section in this first embodiment stores informationby controlling the electric current flowing through the interior of thesemiconductor substrate 10 which underlies the memory gate electrode 26on the basis of whether there is an electric charge stored in the chargestorage film 25. That is, information is stored by utilizing the factthat a threshold voltage of the electric current flowing through theinterior of the semiconductor substrate 10 which underlies the memorygate electrode 26 varies depending on whether an electric charge isstored in the charge storage film 25.

In this first embodiment, an insulating film having a trap level is usedas the charge storage film 25. A silicon nitride film is mentioned as anexample of the insulating film having a trap level, provided nolimitation is made thereto, but there also may be used, for example, analuminum oxide film (alumina). In case of using the insulating filmhaving a trap level as the charge storage film 25, the electric chargeis trapped to the trap level formed in the insulating film and isthereby stored in the insulating film.

Heretofore, a polysilicon film has mainly been used as the chargestorage film 25, but in case of using a polysilicon film as the chargestorage film 25, if there is a defect in part of the silicon oxide film17 or 19 which surrounds the charge storage film 25, all the electriccharge stored in the charge storage film 25 may all be gone due toabnormal leak because the charge storage film 25 is a conductor film.

To avoid such an inconvenience, a silicon nitride film which is aninsulator has been used. In this case, an electric charge whichcontributes to the storage of data is stored to a discrete trap level(capture level) which is present within the silicon nitride film.Therefore, even if a defect occurs in part of the silicon oxide film 17or 19 which surrounds the charge storage film 25, there is no fear thatall the electric charge may be gone from the charge storage film 25,because the electric charge is stored to the discrete trap level.Consequently, it is possible to improve the reliability of data hold.

For such a reason, by using as the charge storage film 25 not only thesilicon nitride film but also such a film as includes a discrete traplevel it is possible to improve the reliability of data hold.

The memory gate electrode 26 is formed on one of the side walls of thecontrol gate electrode 15 and a side wall 29 a comprised of a siliconoxide film is formed on the other side wall. Likewise, the control gateelectrode 15 is formed on one of the side walls of the memory gateelectrode 26 and a side wall 29 a comprised of a silicon oxide film isformed on the other side wall.

A pair of shallow impurity diffusion regions 28 of a low concentration,which are n-type semiconductor regions, are formed within thesemiconductor substrate 10 just underlying the side walls 29 a, and apair of deep impurity diffusion regions 30 of a high concentration areformed in outer regions in contact with the pair of shallow impuritydiffusion regions 28 of a low concentration. The deep impurity diffusionregions 30 of a high concentration are also n-type semiconductor regionsand a cobalt silicide film 33 is formed on a surface of each impuritydiffusion region 30. With the pair of impurity diffusion regions 28 of alow concentration and the pair of impurity diffusion regions 30 of ahigh concentration, there are formed a source region and a drain regionof the memory cell. By forming source and drain regions with use theimpurity diffusion regions of a low concentration and the impuritydiffusion regions 30 of a high concentration, the source and drainregions can be made an LDD (Lightly Doped Drain) structure. A transistorcomprised of the gate insulating film 13, the control gate electrode 15formed thereon and the source and drain regions just described above ishere designated a select transistor. On the other hand, a transistorcomprised of the laminate of the silicon oxide film 17, charge storagefilm 25 and silicon oxide film 19, as well as a memory gate electrode 24formed on the laminate and the source and drain regions described above,is here designated a memory transistor. Thus, it can be said that theselect section of the memory cell is comprised of a select transistor,while the memory section of the memory cell is comprised of a memorytransistor.

Next, a description will be given about a wiring structure coupled tothe memory cell. An interlayer insulating film 34 comprised of a siliconoxide film is formed over the memory cell so as to cover the memorycell. Contact holes 35 are formed through the interlayer insulating film34 so as to reach the cobalt silicide film 33 which configures sourceand drain regions. In the interior of each contact hole 35, atitanium/titanium nitride film 36 a as a barrier conductor film isformed and a tungsten film 36 b is formed so as to fill up the contacthole. By thus burying the titanium/titanium nitride film 36 a and thetungsten film 36 b into each contact hole 35 there is formed anelectrically conductive plug 37 a. A wiring line HL1 is formed over theinterlayer insulating film 34 and is coupled to the plug 37 aelectrically. For example, the wiring line HL1 is formed by a laminateof a titanium/titanium nitride film 38 a, an aluminum film 38 b and atitanium/titanium nitride film 38 c.

The memory cell used in this first embodiment is configured as above andthe following description is now provided about the operation of thememory cell. It is here assumed that the voltage applied to the controlgate 15 is Vcg and the voltage applied to the memory gate 26 is Vmg. Itis further assumed that voltages applied to the source and drainregions, respectively, are Vs and Vd and the voltage applied to thesemiconductor substrate 10 (p-type well 12) is Vb. Injection ofelectrons to the silicon nitride film as the charge storage film isdefined as “write” and injection of holes to the silicon nitride film isdefined as “erase.”

A description will be given first about write operation. Write operationis performed by hot electron write which is called a source-sideinjection method. For example, as write voltages, the voltage Vs appliedto the source region is 6V, the voltage Vmg applied to the memory gateelectrode 26 is 12V, and the voltage Vcg applied to the control gateelectrode 15 is 1.5V. The voltage Vd applied to the drain region iscontrolled so as to become a set value assuming the presence of achannel current in write operation. At this time the voltage Vd isdetermined by both a set value of a channel current and a thresholdvoltage of the select transistor having the control gate electrode 15and is, for example, about 1V. The voltage Vb applied to the p-type well12 (semiconductor substrate 10) is 0V.

Reference will now be made to the behavior of an electric charge at thetime of performing the write operation under application of suchvoltages. As noted above, by giving a potential difference between thevoltage Vs applied to the source region and the voltage Vd applied tothe drain region, electrons flow through a channel region formed betweenthe source region and the drain region. The electrons flowing throughthe channel region is accelerated in the channel region (between thesource and drain regions) located under the vicinity of the boundarybetween the control gate electrode 15 and the memory gate electrode 26and become hot electrons. Then, with a vertical electric field inducedby the positive voltage (Vmg=12V) applied to the memory gate 26, hotelectrons are injected into the silicon nitride film 18 (charge storagefilm 25) which underlies the memory gate electrode 26. The hot electronsthus injected are trapped to the trap level in the silicon nitride film18. As a result, electrons are stored in the silicon nitride film andthe threshold voltage of the memory transistor rises. In this way thereis performed write operation.

The following description is now provided about erase operation. Forexample, erase operation is performed by BTBT (Band to Band Tunneling)which uses a band-to-band tunneling phenomenon. In BTBT erase, forexample, the voltage Vmg applied to the memory gate electrode is −6V,the voltage Vs applied to the source regions is 6V, the voltage Vcgapplied to the control gate electrode is 0V, and 0V is applied to thedrain region. With voltage applied between the source region and thememory gate electrode, holes generated by the band-to-band tunnelingphenomenon at a source region end are accelerated by the high voltageapplied to the source region and become hot holes. Then, a portion ofthe hot holes are attracted to the negative voltage applied to thememory gate electrode 26 and are injected into the silicon nitride film18. The hot holes thus injected are trapped to the trap level in thesilicon nitride film 18, with consequent lowering of the thresholdvoltage of the memory transistor. In this way there is performed eraseoperation.

The following description is now provided about read operation. Readoperation is performed by setting the voltage Vd to be applied to thedrain region at Vdd (1.5V), the voltage Vs to be applied to the sourceregion at 0V, the voltage Vcg to be applied to the control gateelectrode at Vdd (1.5V), the voltage Vmg to be applied to the memorygate electrode at Vdd (1.5V) and by passing an electric current in adirection opposite to the direction in write operation. The voltage Vdapplied to the drain region and the voltage Vs applied to the sourceregion are interchanged into 0V and 1.5V, respectively, and readoperation may be done in the same direction of an electric current asthe direction in write operation. At this time, if the memory cell is ina state of write and the threshold voltage is high, there flows noelectric current in the memory cell. On the other hand, if the memorycell is in a state of erase and the threshold voltage is low, thereflows an electric current in the memory cell.

Thus, whether the memory cell is in a state of write or in a state oferase can be determined by detecting whether an electric current isflowing or not in the memory cell. More specifically, whether anelectric current is flowing or not in the memory cell is detected by asense amplifier. For example, a reference current is used to detectwhether there is an electric current flowing in the memory cell. Thatis, when the memory cell is in a state of erase, a read current flows inread operation, which read current is compared with the referencecurrent. The reference current is set lower than the read current in astate of erase, and if the read current is found larger than thereference current as a result of comparison between the read current andthe reference current, it can be determined that the memory cell is in astate of erase. On other hand, when the memory cell is in a state ofwrite, a read current does not flow. That is, when the read current isfound smaller than the reference current as a result of comparisonbetween the read current and the reference current, it can be determinedthat the memory cell is in a state of write. In this way it is possibleto perform read operation.

In the memory transistor a laminate film is formed between the memorygate electrode 26 and the semiconductor substrate 10. This laminate filmis comprised of the silicon oxide film 17, charge storage film 25 andsilicon oxide film 19. Write and erase operations in the memorytransistor are performed by the injection of an electric charge into thecharge storage film 25. For example, as described above, write operationis performed by injection of electrons into the charge storage film 25and erase operation is performed by injection of holes into the chargestorage film 25. In a state of write, the threshold voltage of thememory transistor is in a raised state by electron injection into thecharge storage film 25. At this time, electrons are stored on thecontrol gate electrode 15 side of the charge storage film 25. That is,the electrons stored in the charge storage film 25 are localized in alimited region of the charge storage film 25.

On the other hand, in a state of erase, the threshold voltage of thememory transistor is in a lowered state as a result of injection ofholes into the charge storage film 25. At this time, the holes arestored in the source side (the right-hand impurity diffusion region 28of a low concentration) of the charge storage film 25. Therefore, theholes are also localized in a limited region of the charge storage film25. In erase operation, the electrons present within the charge storagefilm 25 are extinguished to lower the threshold value by pair extinctionof holes with the electrons injected and stored into the charge storagefilm 25. However, as noted above, the localized region of electrons andthat of holes are different, so if the width of the charge storage film25 is large, it becomes difficult to effect an efficient pair extinctionbetween electrons and holes and the reliability of the memory transistoris deteriorated. In the memory cell (memory transistor) the polysiliconfilm 20 is made thin to solve this problem. As a result, the gate lengthof the memory gate electrode 26 becomes short and therefore the width ofthe charge storage film 25 formed under the memory gate electrode 26also becomes small. Consequently, the localized region of electrons andthat of holes in the charge storage film 25 come close to each other,whereby the pair extinction of electrons and holes is carried out to asatisfactory extent and there is obtained an effect that the reliabilityof the memory transistor is improved.

The configuration and operation of the memory cell have been describedabove. Next, a description will be given about the configuration of thePIP capacitor element. The configuration of the PIP capacitor element isthe same as that shown in FIGS. 3 and 4. In FIG. 6, Capacitor ElementForming Region (A-A) is shown in a sectional view corresponding to FIG.3 and Capacitor Element Forming Region (B-B) is shown in a sectionalview corresponding to FIG. 4. In FIG. 6 there is shown a case where thememory cell and the PIP capacitor element are formed in the memory cellforming process and therefore the configuration of the PIP capacitorelement will be described below from the standpoint of explaining acorrelation between constituent elements of the memory cell and those ofthe PIP capacitor element.

In FIG. 6, an element isolation region 11 is formed on a semiconductorsubstrate 10. The element isolation region is a region for separatingelements electrically. For example, it is formed for separation betweena high voltage-proof MISFET and a low voltage-proof MISFET. The elementisolation region 11 is formed also in the capacitor element-formingregion. The element isolation region 11 formed in the capacitorelement-forming region has a function of isolating the PIP capacitorelement formed in the element isolation region 11 from the semiconductorsubstrate 10. That is, the PIP capacitor element is formed on theelement isolation region 11.

A gate insulating film 13 is formed on the element isolation region 11and a lower electrode 16 of the capacitor element is formed on the gateinsulating film 13. The lower electrode 16 is formed of a polysiliconfilm 14. The lower electrode 16 is formed by the same film as thepolysilicon film 14 which configures the control gate electrode 15formed in the memory cell-forming region. That is, the lower electrode16 of the PIP capacitor element is formed simultaneously in the processof forming the control gate electrode 15 of the memory cell, althoughthis point will be described later in connection with the manufacturingmethod.

A capacitor insulating film 27 is formed on the lower electrode 16. Thecapacitor insulating film 27 is comprised of a silicon oxide film 17, asilicon nitride film 18 formed on the silicon oxide film, and a siliconoxide film 19 formed on the silicon nitride film 18. That is, thecapacitor insulating film 27 is formed by the same film as the laminatefilm which configures the memory transistor of the memory cell. In otherwords, in the capacitor element-forming region, the laminate comprisedof the silicon oxide film, charge storage film 25 (silicon nitride film18) and silicon oxide film 19 in the memory cell serves as the capacitorinsulating film 27 of the capacitor element.

An upper electrode 23 is formed on the capacitor insulating film 27. Theupper electrode 23 is comprised of a polysilicon film 20 and a cobaltsilicide film 33. The polysilicon film 20 is a constituent film of thememory gate electrode 26 of the memory cell. That is, the polysiliconfilm 20 as a constituent of the upper electrode 23 is formedsimultaneously in the process of forming the memory gate electrode 26 ofthe memory cell.

In the memory cell (memory transistor), as noted above, the thickness ofthe polysilicon film 20 is made small from the standpoint of improvingthe reliability of the memory cell. That is, the gate length of thememory gate electrode 26 is made small by thinning the polysilicon film20. This is for suppressing localization of electrons and holes andthereby promoting a pair extinction of electrons and holes. Thepolysilicon film 20 is also used as the upper electrode 23 of the PIPcapacitor element. Therefore, by thinning of the polysilicon film 20 ismeant thinning of the film of the upper electrode 23 in the PIPcapacitor element.

Consequently, in the PIP capacitor element formed in the same process asthe memory cell, the polysilicon film 20 as a constituent of the upperelectrode 23 is becoming more and more thin. Particularly, ashort-circuit defect caused by abnormal growth of the cobalt silicidefilm 33 is becoming conspicuous as a problem. Thus, in the PIP capacitorelement including an overlapping region and non-overlapping regions asregions for forming the upper electrode 23, a short-circuit defectcaused by abnormal growth of the cobalt silicide film 33 poses aproblem. It is seen that particularly in the PIP capacitor elementformed in the same process as the memory cell it is important to take anappropriate countermeasure because the film thickness of he upperelectrode 23 becomes smaller.

In this first embodiment, as shown in FIG. 6 (see Capacitor ElementForming Region (A-A)), end portions of the cobalt silicide film 33formed on the upper electrode 23 are spaced apart a distance L1 from endportions of the upper electrode 23. By so doing there is obtained aneffect that it is possible to prevent the cobalt silicide film 33 fromreaching the end portions of the upper electrode 23 and creeping out toside walls 29 b. Besides, end portions of the cobalt silicide film 33formed on the lower electrode 16 are spaced apart a distance L2 fromboundaries between the upper electrode 23 and the lower electrode 16. Inthis case, even if the cobalt silicide film 33 grows abnormally andcreeps out to the side walls 29 b, the cobalt silicide film 33 formed onthe lower electrode 16 is spaced apart from the side walls 29 b.Accordingly, there is obtained an effect that it is possible to preventcontact between the cobalt silicide film 33 creeping out along the sidewalls 29 b and the cobalt silicide film formed on the lower electrode16.

Further, as sown in FIG. 6 (see Capacitor Element Forming Region (B-B)),the cobalt silicide film 33 is formed neither within the ranges ofdistance L3 from stepped regions toward an overlapping region in theupper electrode 23 nor within the ranges of distance L4 from the steppedregions toward non-overlapping regions (side walls 29 d-formed regions).Thus, since the cobalt silicide film is not formed at upper end portionsof the stepped regions, it is possible to eliminate the influence causedby field concentration in the stepped regions and the influence of ashorter distance between the cobalt silicide film and the capacitorinsulating film 27.

Next, a semiconductor device manufacturing method according to thisfirst embodiment will be described below with reference to drawings.

First, as shown in FIG. 7, there is provided a semiconductor substrate10 of a single crystal silicon with a p-type impurity such as boron (B)introduced therein. At this time, the semiconductor substrate 10 is in astate of a generally disc-like semiconductor wafer. Then, there isformed an element isolation region for isolation between a lowvoltage-proof MISFET forming region and a high voltage-proof MISFETforming region of the semiconductor substrate 10. The element isolationregion is formed so as to avoid mutual interference of the elements. Theelement isolation region can be formed, for example, by LOCOS (localoxidation of silicon) method or STI (shallow trench isolation) method.For example, the element isolation region is formed by STI method in thefollowing manner. An element isolation trench is formed in thesemiconductor substrate 10 with use of the photolithography technique oretching technique. Then, a silicon oxide film is formed on thesemiconductor substrate 10 so as to fill up the element isolation trenchand thereafter unnecessary silicon oxide film formed on thesemiconductor substrate 10 is removed by CMP (chemical mechanicalpolishing) method. As a result, there can be formed an element isolationregion with silicon oxide film buried into only the element isolationtrench. In FIG. 7, an element isolation region 11 is not formed in thememory cell-forming region, but it is formed in the capacitorelement-forming region.

Subsequently, a p-type well 12 is formed by introducing an impurity intothe semiconductor substrate 10. The p-type well 12 can be formed byintroducing a p-type impurity, e.g., boron, into the semiconductorsubstrate 10 by an ion implantation method. In the memory cell-formingregion, a semiconductor region (not shown) for forming a channel of aselect transistor is formed in a surface region of the p-type well 12.This channel forming semiconductor region is formed for adjusting achannel-forming threshold voltage.

Next, as shown in FIG. 8, a gate insulating film 13 is formed on thesemiconductor substrate 10. The gate insulating film 13, which is forexample a silicon oxide film, can be formed for example by a thermaloxidation method. However, the gate insulating film 13 is not limited tothe silicon oxide film, but various changes may be made. For example,the gate insulating film 13 may be a silicon oxynitride film (SiON).That is, there may be adopted a structure wherein nitrogen is segregatedat the interface between the gate insulating film 13 and thesemiconductor substrate 10. In comparison with the silicon oxide film,the silicon oxynitride film is highly effective in suppressing thegeneration of an interface level within the film and diminishingelectron trap. Therefore, it is possible to improve the hot carrierresistance and dielectric strength of the gate insulating film 13.Moreover, impurities are difficult to penetrate the silicon oxynitridefilm in comparison with the silicon oxide film. Therefore, by using thesilicon oxynitride film as the gate insulating film 13 it is possible tosuppress variation of the threshold voltage caused by diffusion of theimpurity present within the gate electrode to the semiconductorsubstrate 10 side. The silicon oxynitride film can be formed for exampleby heat-treating the semiconductor substrate 10 in an atmospherecontaining nitrogen such as NO, NO₂ or NH₃. The same effect can beobtained also by forming a silicon oxide film as the gate insulatingfilm 13 on a surface of the semiconductor substrate 10 and thereafterheat-treating the semiconductor substrate 10 in a nitrogen-containingatmosphere, allowing segregation of nitrogen to take place at theinterface between the gate insulating film 13 and the semiconductorsubstrate 10.

The gate insulating film 13 may be formed for example by a film higherin dielectric constant than the silicon oxide film. Heretofore, thesilicon oxide film has been used from the standpoint that the dielectricstrength is high and that the silicon-silicon oxide interface is high inelectrical and physical stability. However, with microminiaturization ofelements, there now exists a demand for an ultra-thin film as the gateinsulating film 13. If such a thin silicon oxide film is used as thegate insulating film 13, electrons flowing through the MISFET channeltunnel a barrier formed by the silicon oxide film and flow to the gateelectrode. Thus, a so-called tunnel current is generated.

In view of this point, by using a material higher in dielectric constantthan the silicon oxide film there is formed a high dielectric filmcapable of being increased in physical thickness even under the samecapacity and this high dielectric film has come to be used. With thehigh dielectric film, it is possible to diminish leak current because aphysical film thickness can be increased even under the same capacity.

For example, a hafnium oxide film (HfO₂ film), which is one of hafniumoxides, is used as a high dielectric film, but in place of the hafniumoxide film there may be used any of other hafnium-based insulating filmssuch as, for example, hafnium aluminate film, HfON film (hafniumoxynitride film), HfSiO film (hafnium silicate film), HfSiON film(hafnium silicon oxynitride film) and HfAlO film. Further, such oxidesas tantalum oxide, niobium oxide, titanium oxide, zirconium oxide,lanthanum oxide and yttrium oxide may be introduced into thosehafnium-based insulating films and the resulting hafnium-basedinsulating films may also be used. Like the hafnium oxide film, thehafnium-based insulating films are higher in dielectric constant thanthe silicon oxide film and silicon oxynitride film, so there is obtainedthe same effect as in the use of the hafnium oxide film.

Then, a polysilicon film 14 is formed on the gate insulating film 13.The polysilicon film 14 can be formed, for example, by CVD method.Further, an n-type impurity such as phosphorus or arsenic is introducedinto the polysilicon film 14 with use of the photolithography techniqueand ion implantation method.

Next, as shown in FIG. 9, the polysilicon film 14 is etched using apatterned resist film as a mask to form a control gate electrode 15 inthe memory cell-forming region and a lower electrode 16 in the capacitorelement-forming region. The control gate electrode 15 is a gateelectrode of the select transistor in the memory cell. Thus, it is seenthat the lower electrode 16 of the capacitor element is formed in theprocess of forming the control gate electrode 15 of the memory cell.

In the control gate electrode 15, an n-type impurity is introduced intothe polysilicon film 14, so that a work function value of the controlgate electrode 15 can be made a value (4.15 eV) close to the conductionband of silicon. Consequently, it is possible to decrease the thresholdvoltage of the select transistor which is an n-channel type MISFET.

Subsequently, though not shown, an n-type impurity such as phosphorus orarsenic is introduced to match the control gate electrode 15 with use ofthe photolithography technique or ion implantation method. As will bedescribed later, this process is carried out for adjusting the thresholdvalue of a memory transistor formed on side walls of the control gateelectrode 15.

Next, as shown in FIG. 10, a laminate film is formed over thesemiconductor substrate 10 so as to cover the control gate electrode 15and the lower electrode 16. The laminate film is comprised of, forexample, a silicon oxide film 17, a silicon nitride film 18 formed onthe silicon oxide film 17, and a silicon oxide film 19 formed on thesilicon nitride film 18, (ONO film). The laminate film can be formed byCVD method for example. The thickness of the silicon oxide film 17, thatof the silicon nitride film 18, and that of the silicon oxide film 19,are set at, for example, 5 nm, 10 nm, and 5 nm, respectively.

In this laminate film, the silicon nitride film 18 serves as a chargestorage film of the memory transistor in the memory cell-forming region.Although in this first embodiment the silicon nitride film 18 is used asthe charge storage film, another insulating film having a trap level maybe used as the charge storage film. For example, an aluminum oxide film(alumina film) may be used as the charge storage film. The laminate filmserves as a capacitor insulating film in the capacitor element-formingregion.

Then, a polysilicon film 20 is formed on the laminate film, for example,by CVD method.

Next, as shown in FIG. 11, a resist film 21 is applied onto thesemiconductor substrate 10 and is then subjected to exposure anddevelopment to effect patterning. The patterning is performed so as tocover the upper electrode-forming region in the capacitorelement-forming region and expose the other region.

Subsequently, as shown in FIG. 12, the polysilicon film 20 is subjectedto anisotropic etching with the resist film 21 as a mask, therebyallowing side walls 22 a and 22 b to remain on both side wallsrespectively of the control gate electrode 15. On the other hand, in thecapacitor element-forming region, the polysilicon film 20 remains inonly the region that has been covered with the resist film 21, and anupper electrode 23 is formed by the remaining polysilicon film 20. Atthis stage the upper electrode 23 is comprised of the polysilicon film20. Thereafter, the resist film 21 after patterning is removed. In A-Asection the length of the upper electrode 23 is shorter than that of thelower electrode 16, while in B-B section the length of the upperelectrode 23 is larger than that of the lower electrode 16. Thus, as isseen from B-B section, there are formed a planarly overlapping region ofboth upper and lower electrodes 23, 16 and non-overlapping regions wherethe upper and lower electrodes 23, 16 do not planarly overlap eachother.

Then, as shown in FIG. 13, a resist film 24 is applied onto thesemiconductor substrate 10 and is thereafter subjected to exposure anddevelopment to effect patterning of the resist film. The patterning isperformed so as to cover the capacitor element-forming region completelyand open a part of the memory cell-forming region. More specifically,the patterning is performed in such a manner that the side wall 22 bformed on one side wall of the control gate electrode 15 in the memorycell-forming region is exposed. For example, in FIG. 13, the side wall22 b formed on the left side wall of the control gate electrode 15 inthe memory cell-forming region is exposed.

Next, as shown in FIG. 14, the side wall 22 b exposed on the left sidewall of the control gate electrode 15 is removed by etching with use ofthe patterned resist film 24 as a mask. At this time, the side wall 22 aformed on the right side wall of the control gate electrode 15 is notremoved because it is covered with the resist film 24. Also in thecapacitor element-forming region the upper electrode 23 remains withoutbeing removed because it is protected by the resist film 24. Thereafter,the patterned resist film 24 is removed.

Subsequently, as shown in FIG. 15, the exposed ONO film (laminate film)is removed by etching. In this way, in the memory cell-forming region, amemory gate electrode 26 of a side wall shape is formed on only theright side wall of the control gate electrode 15 through the laminatefilm (ONO film). At this time, the silicon nitride film 18 as aconstituent of the laminate film (ONO film) serves as a charge storagefilm 25. On the other hand, in the capacitor element-forming region,only the ONO film covered with the upper electrode 23 remains and theONO film which underlies the upper electrode 23 serves as a capacitorinsulating film 27. That is, the capacitor insulating film 27 iscomprised of the silicon oxide film 17, silicon nitride film 18 andsilicon oxide film 19. At this stage, the memory gate electrode 26 ofthe memory cell and the upper electrode 23 of the capacitor element areeach formed by the polysilicon film.

Next, as shown in FIG. 16, in the memory cell-forming region, shallowimpurity diffusion regions 28 of a low concentration matching thecontrol gate electrode 15 and the memory gate electrode 26, are formedwith use of the photolithography technique and ion implantation method.The shallow impurity diffusion regions 28 of a low concentration aren-type semiconductor regions with an n-type impurity such as phosphorusor arsenic introduced therein.

Then, as shown in FIG. 17, a silicon oxide film is formed on thesemiconductor substrate 10, for example, by CVD method. Further, thesilicon oxide film is subjected to anisotropic etching to form sidewalls. In the memory cell-forming region, side walls 29 a are formed onthe left side wall of the control gate electrode 15 and the right sidewall of the memory gate electrode 24, respectively. On the other hand,in the capacitor element-forming region (A-A section), side walls 29 bare formed on side walls of the upper electrode 23 and the capacitorinsulating film 27 and side walls 29 c are formed on side walls of thelower electrode 16. Likewise, in the capacitor element-forming region(B-B), side walls 29 d are formed in stepped regions of the upperelectrode 23 and side walls 29 e are formed in end regions of the upperelectrode 23. The side walls 29 a to 29 e are each formed by a singlesilicon oxide film, provided no limitation is made thereto. For example,a side wall comprised of a laminate of both silicon nitride film andsilicon oxide film may be formed.

Next, as shown in FIG. 18, deep impurity diffusion regions 30 of a highconcentration matching the side walls 29 a are formed in the memorycell-forming region with use of the photolithography technique and ionimplantation method. The deep impurity diffusion regions 30 of a highconcentration are n-type semiconductor regions with an n-type impuritysuch as phosphorus or arsenic introduced therein. Source and drainregions of the memory cell are formed by the deep impurity diffusionregions 30 of a high concentration and the shallow impurity diffusionregions 28 of a low concentration. By thus forming the source and drainregions with the shallow impurity diffusion regions 28 of a lowconcentration and the deep impurity diffusion regions 30 of a highconcentration, the source and drain regions can be made to have an LDD(Lightly Doped Drain) structure. After the impurity diffusion regions 30of a high concentration are thus formed, there is performed a heattreatment at a temperature of about 1000° C., whereby the introducedimpurity is activated.

Subsequently, as shown in FIG. 19, a silicon oxide film 31 is formed onthe semiconductor substrate 10 and a resist film is formed on thesilicon oxide film 31, followed by exposure and development to effectpatterning. As shown in the capacitor element-forming region (A-Asection), the patterning is performed in such a manner that resist filmportions 32 a are allowed to remain so as to cover predetermined rangesincluding end regions of the upper electrode 23. Likewise, as shown inthe capacitor element-forming region (B-B section), the patterning isperformed in such a manner that resist film portions 32 b are allowed toremain so as to cover predetermined ranges including stepped regionslocated at boundaries between the overlapping region and non-overlappingregions of the upper electrode 23.

Thereafter, as shown in FIG. 20, etching is performed with the resistfilms 32 a and 32 b as masks to pattern the silicon oxide film 31. As aresult, as shown in the capacitor element-forming region (A-A section),the silicon oxide film 31 is formed so as to cover the regions spacedapart the distance L1 from end portions of the upper electrode 23 towardthe inside of the upper electrode 23 and also cover the regions spacedapart the distance L2 from end portions of the upper electrode 23 towardthe side walls 29 b. Further, as shown in the capacitor element-formingregion (B-B section), the silicon oxide film 31 is formed so as to coverthe regions spaced apart the distance L3 from the stepped regions towardthe overlapping region of the upper electrode 23 and also cover theregions spaced apart the distance L4 from the stepped regions toward thenon-overlapping regions (lead-out regions) of the upper electrode 23.

Next, as shown in FIG. 21, a cobalt film is formed on the semiconductorsubstrate 10. At this time, in the memory cell-forming region, thecobalt film is formed so as to come into direct contact with the exposedcontrol gate electrode 15 and memory gate electrode 24. Likewise, thecobalt film comes into contact also with the deep impurity diffusionregions 30 of a high concentration. On the other hand, in the capacitorelement-forming region, the cobalt film comes into direct contact withpart of the lower electrode 16 and part of the upper electrode 22,provided the cobalt film is put in direct contact with neither theregions spaced apart the distance L1 from end portions of the upperelectrode 23 toward the inside of the upper electrode nor the regionsspaced apart the distance L2 from end portions of the upper electrode 23toward the side walls 29 b because these regions are covered with thesilicon oxide film 31. Likewise, the cobalt film is put in directcontact with neither the regions spaced apart the distance L3 from thestepped regions toward the overlapping region of the upper electrode 23nor the regions spaced apart the distance L4 from the stepped regionstoward the non-overlapping regions (lead-out regions) of the upperelectode 23 because these regions are covered with the silicon oxidefilm 31. The cobalt film can be formed, for example, by sputtering. Thethickness of the cobalt film is, for example, 10 nm.

Then, a first heat treatment is performed for the semiconductorsubstrate 10 and thereafter the surface of the semiconductor substrate10 is cleaned. This cleaning is done by both APM (Ammonium hydroxidehydrogen Peroxide Mixture) cleaning and HPM cleaning. APM cleaning usesa mixed solution consisting of ammonium hydroxide (NH₄OH), hydrogenperoxide (H₂O₂) and pure water (H₂O), which is highly effective inremoving particles and organic matters. On the other hand, HPM cleaninguses a mixed solution consisting of hydrochloric acid (HCl), hydrogenperoxide (H₂O₂) and pure water (H₂O), which is highly effective inremoving metals. After the cleaning, a second heat treatment isperformed. As a result, in the memory cell-forming region, as shown inFIG. 21, the polysilicon films 14 and 20 which configure the controlgate electrode 15 and the memory gate electrode 26, respectively, andthe cobalt film are reacted with each other to form a cobalt silicidefilm 31. Consequently, the control gate electrode 15 and the memory gateelectrode 26 become laminates of the polysilicon films 14, 20,respectively, and the cobalt silicide film 31. The cobalt silicide film31 is formed for making the control gate 15 and the memory gateelectrode 26 low in resistance. Likewise, by the above heat treatment,also on the surface of the impurity diffusion regions 30 of a highconcentration, silicon and the cobalt film react with each other to forma cobalt silicide film 33. Consequently, it is possible to attain a lowresistance also in the impurity diffusion regions 30 of a highconcentration.

On the other hand, in the capacitor element-forming region, a cobaltsilicide film 33 is formed in part of the upper electrode 23 and also inpart of the lower electrode 16 whose surfaces are not covered with thesilicon oxide film 31. In the region covered with the silicon oxide film31 the cobalt silicide film 33 is not formed because the silicidationreaction does not proceed. For example, in the capacitor element-formingregion (A-A section), the cobalt silicide film 33 is formed neither inthe regions spaced apart the distance L1 from end portions of the upperelectrode 23 toward the inside of the upper electrode nor in the regionsspaced apart the distance L2 from end portions of the upper electrode 3toward the side walls 29 b. Therefore, at the end portions of the upperelectrode 23 it is possible to prevent abnormal growth of the cobaltsilicide film 33 because the same film is not present. Consequently, itis possible to prevent a short-circuit defect between the upperelectrode 23 and the lower electrode 16 which is caused by abnormalgrowth of the cobalt silicide film 33.

Further, for example in the capacitor element-forming region (B-Bsection), the cobalt silicide film 33 is formed neither in the regionsspaced apart the distance L3 from the stepped regions toward theoverlapping region of the upper electrode 23 nor in the regions spacedapart the distance L4 from the stepped regions toward thenon-overlapping regions (lead-out regions) of the upper electrode.Therefore, it is possible to eliminate the influence caused by fieldconcentration in the stepped regions and the influence of a shorterdistance between the cobalt silicide film 33 and the capacitorinsulating film 27. Thus, in the PIP capacitor element according to thisfirst embodiment it is possible to prevent dielectric breakdown of thecapacitor insulating film 27.

Unreacted cobalt film is removed from the surface of the semiconductorsubstrate 10. Although the cobalt silicide film 33 is formed in thisfirst embodiment, it may be substituted by, for example, a nickelsilicide film or a titanium silicide film.

In the manner described above it is possible to form the memory cell inthe memory cell-forming region and also form the PIP capacitor elementaccording to this first embodiment in the capacitor element-formingregion.

Next, a wiring process will be described with reference to FIG. 6. Asshown in the same figure, an interlayer insulating film 34 is formed ona main surface of a semiconductor substrate 10. The interlayerinsulating film 34 is formed, for example, by a silicon oxide film. Forexample, it can be formed by CVD method using TEOS (tetra ethyl orthosilicate) as a raw material. Thereafter, the surface of the interlayerinsulating film 34 is planarized, for example, by CMP (ChemicalMechanical Polishing) method.

Subsequently, contact holes 35 are formed in the interlayer insulatingfilm 34 with use of photolithography technique and etching technique.Plural contact holes 35 are formed in the memory cell-forming region andthe capacitor element-forming region. Then, a titanium/titanium nitridefilm 36 a is formed on the interlayer insulating film 34, includingbottoms and inner walls of the contact holes 35. The titanium/titaniumnitride film 36 a is comprised of a laminate of both titanium film andtitanium nitride film and it can be formed, for example, by sputtering.The titanium/titanium nitride film 36 a functions as a so-called barrierfor example to prevent tungsten as the material of a film to be buriedin a later process from being diffused into silicon.

Then, a tungsten film 36 b is formed throughout the whole of the mainsurface of the semiconductor substrate 10. For example, it can be formedby CVD method. Further, unnecessary titanium/titanium nitride film 36 aand tungsten film 36 b formed on the interlayer insulating film 34 areremoved, for example, by CMP method, whereby plugs 37 a to 37 c can beformed.

Next, a titanium/titanium nitride film 38 a, an aluminum film 38 bcontaining copper, and a titanium/titanium nitride film 38 c are formedin this order onto the interlayer insulating film 34 and the plugs 37 ato 37 c. These films can be formed, for example, by sputtering.Subsequently, these films are subjected to patterning with use ofphotolithography technique and etching technique to form wiring linesHL1, HL2 and HL3. Further, wiring is formed over wiring, but anexplanation on this point will here be omitted. In this way it ispossible to eventually fabricate the semiconductor device according tothis first embodiment.

Second Embodiment

In the above first embodiment a description has been given about asingle PIP capacitor element, while in this second embodiment adescription will be given about using an upper electrode in common forplural PIP capacitor elements.

FIG. 22 is a plan view showing a PIP capacitor element according to thissecond embodiment. In the same figure, a lower electrode (first lowerelectrode) 16 a and a lower electrode (second lower electrode) 16 b arearranged side by side spacedly in y direction and a common upperelectrode 23 is formed over the lower electrodes 16 a and 16 b.

The lower electrodes 16 a and 16 b have the same rectangular shape. Onthe other hand, the lower electrodes 16 a, 16 b and the upper electrode23 are in rectangular shapes different from each other and have planarlyoverlapping regions and planarly non-overlapping regions. As shown inFIG. 22, the lower electrodes 16 a and 16 b are each longer than theupper electrode 23 in x direction, while in y direction (directionintersecting the x direction) the length of the upper electrode 23 islarger than the sum of the length of the lower electrode 16 a and thatof the lower electrode 16 b. One PIP capacitor element is formed in aplanarly overlapping region of the lower electrode 16 a and the upperelectrode 23 thus configured. Likewise, one PIP capacitor element isformed in a planarly overlapping region of the lower electrode 16 b andthe upper electrode 23. Thus, in FIG. 22 there are formed two PIPcapacitor elements and the upper electrode 23 is common to those PIPcapacitor elements. In the non-overlapping regions of the lowerelectrodes 16 a and 16 b there are formed plugs 37 b which are coupledelectrically to the lower electrode 16 a or 16 b, while in thenon-overlapping region of the upper electrode 23 there are formed plugs37 c coupled electrically to the upper electrode 23.

As shown in FIG. 22, in the PIP capacitor element according to thissecond embodiment, the non-overlapping region (lead-out region) whichconfigures a part of the upper electrode 23 is formed on only one sidewith respect to each of the lower electrodes 16 a and 16 b. This pointis different from the previous first embodiment. By thus making helead-out region (non-overlapping region) common on one side of each ofthe lower electrodes 16 a and 16 b there is obtained an effect that thearea occupied by the PIP capacitor elements can be reduced. Moreover, bycoupling plural PIP capacitor elements in parallel, a PIP capacitorelement of a large capacity can be realized by a small occupancy area.Plural PIP capacitor elements can be coupled in parallel by making theseparated lower electrodes 16 a and 16 b equal in potential. On theother hand, as to the upper electrode 23, it is inevitably at the samepotential because it is made common.

Also in the PIP capacitor elements thus configured there arises the sameproblem as in the previous first embodiment because the basicconfiguration thereof is the same as in the first embodiment. Therefore,the same configuration as in the first embodiment is adopted also inthis second embodiment. In FIG. 22, hatched regions defined by distancesL1 and L2 are shown in boundary regions between the upper electrode 23and the lower electrodes 16 a, 16 b. Further, hatched regions defined bydistances L3+L4 are shown in boundary regions (stepped regions) betweenoverlapping regions and non-overlapping region of the upper electrode23. A cobalt silicide film is not formed in these hatched regions andthis point is a feature of this second embodiment. Consequently, as inthe first embodiment, it is possible to prevent the occurrence of ashort-circuit defect caused by creeping up of the cobalt silicide filmfrom end regions of the upper electrode 23 and reaching the surface ofthe lower electrode 16 and also prevent dielectric breakdown of thecapacitor insulating film caused by field concentration in the steppedregions of the upper electrode 23.

The method for forming the PIP capacitor elements in this secondembodiment is the same as in the previous first embodiment except that achange is made to a mask for implementing such a layout configuration asshown in FIG. 22.

Third Embodiment

Although in the first embodiment there is shown an example of formingthe PIP capacitor element on the element isolation region, in this thirdembodiment a description will be given about a configuration whereinplural PIP capacitor elements are stacked on an electrically conductivesemiconductor substrate.

The planar layout of PIP capacitor elements in the second embodiment isthe same as that shown in FIG. 2 which shows the planar layout of PIPcapacitor element in the first embodiment. A different point betweenthis third embodiment and the first embodiment appears in sectionalviews. FIG. 23 is a sectional view of a PIP capacitor element in thisthird embodiment, which corresponds to the A-A section of FIG. 2. FIG.14 is a sectional view of the PIP capacitor element in this thirdembodiment, which corresponds to the B-B section of FIG. 2. As shown inFIGS. 23 and 24, element isolation regions 11 are formed on asemiconductor substrate 10 and a PIP capacitor element is formed in anactive region sandwiched in between the element isolation regions 11.That is, the PIP capacitor element in this third embodiment includes afirst capacitor element, the first capacitor element including thesemiconductor substrate as a first electrode and a lower electrode 16 asa second electrode, the lower electrode 16 being formed on thesemiconductor substrate through a gate insulating film 13. The gateinsulating film 13 serves as a capacitor insulating film of the firstcapacitor element.

Further, an upper electrode 23 is formed on the lower electrode 16(second electrode) through a capacitor insulating film 27, thusconfiguring a second capacitor element comprising the lower electrode16, capacitor insulating film 27 and upper electrode 23 (thirdelectrode). In this way, in this third embodiment the first and secondcapacitor elements are formed in a vertically stacked fashion. Thus, bycoupling the first and second capacitor elements in parallel it ispossible to form a PIP capacitor element of a large capacitance value atan occupancy area equal to that in the first embodiment. Parallelcoupling between the first and second capacitor elements can beimplemented by making the semiconductor substrate 10 and the upperelectrode 23 equal in potential.

Also in the PIP capacitor element thus configured there arise the sameproblem as in the first embodiment because the basic configurationthereof is the same as in the firs embodiment. Therefore, also in thisthird embodiment there is adopted the same configuration as in the firstembodiment. That is, as shown in FIG. 23, end portions of a cobaltsilicide film 33 formed on the upper electrode 23 are spaced apart thedistance L1 from end portions of the upper electrode 23. According tothis configuration there is obtained an effect that it is possible toprevent the cobalt silicide film 33 from reaching the end portions ofthe upper electrode 23 and creeping out to side walls 29 b. Besides, endportions of the cobalt silicide film 33 are spaced apart the distance L2from boundaries between the upper electrode 23 and the lower electrode16. Consequently, even if the cobalt silicide film 33 grows abnormallyand creeps out to the side walls 29 b, it is possible to prevent contactbetween the cobalt silicide film 33 creeping out along the side walls 29b and the cobalt silicide film formed on the lower electrode 16, becausethe cobalt silicide film 33 formed on the lower electrode 16 is spacedapart from the side walls 29 b.

Further, as shown in FIG. 24, the cobalt silicide film 33 is formedneither in the ranges of distance L3 from stepped regions formed in theupper electrode 23 toward the overlapping region nor in the ranges ofdistance L4 from the stepped regions toward the non-overlapping regions(side walls 29 d-forming regions). Thus, since the cobalt silicide film33 is not formed on upper end portions of the stepped regions, it ispossible to eliminate the influence caused by field concentration in thestepped regions and the influence of a shorter distance between thecobalt silicide film 33 and the capacitor insulating film 27. Therefore,according to the PIP capacitor element in this third embodiment it ispossible to prevent dielectric breakdown of the capacitor insulatingfilm 27.

The method for forming the PIP capacitor element in this thirdembodiment is the same as in the first embodiment except that the PIPcapacitor element is formed on an active region sandwiched in betweenelement isolation regions.

Although the present invention has been described above concretely, itgoes without saying that the present invention is not limited to theabove embodiments and that various changes may be made within the scopenot departing from the gist of the invention.

The present invention is widely applicable to the semiconductor devicemanufacturing industry.

What is claimed is:
 1. A semiconductor device comprising: (a) asemiconductor substrate; (b) an element isolation region formed over thesemiconductor substrate; and (c) a capacitor element formed over theelement isolation region, the capacitor element (c) including: (c1) alower electrode formed over the element isolation region; (c2) acapacitor insulating film formed over the lower electrode; and (c3) anupper electrode formed over the capacitor insulating film, wherein thelength of the upper electrode in a first direction is larger than thatof the lower electrode in the direct direction, the length of the upperelectrode in a second direction intersecting the first direction issmaller than that of the lower electrode in the second direction, thecapacitor element is formed in a region where the upper electrode andthe lower electrode overlap each other planarly, and wherein, over asurface of the upper electrode, there exist a region where a metalsilicide film is formed and a region where the metal silicide film isnot formed, the metal silicide film-formed region comprising a regionspaced apart from an end region of the upper electrode in the seconddirection and a region spaced apart from a stepped region of the upperelectrode in the first direction.